SB 



U. S. DEPARTMENT OF AGRICULTURE. 

BUREAU OF PLANT INDUSTRY— BULLETIN NO. 217. 

B. T. GALLOWAY, Chief of Bureau. 



ROOT-KNOT AND ITS CONTROL. 



ERNST A. BESSEY, 

Professor of Botany, Michigan Agricultural College, and 
Collaborator, Bureau of Plant Industry. 



Issued November 21, 1911. 




WASHINGTON : 

GOVERNMENT PRINTING OFFICE. 

1911. 



U S DEPARTMENT OF AGRICULTURE. 
I 

BUREAU OF PLANT INDUSTRY— BULLETIN NO. 217. 

B. T. GALLOWAY, Chief of Bureau. 



ROOT-KNOT AND ITS CONTROL. 









BY 

y 

ERNST A1BESSEY, 

Professor of Botany, Michigan Agricultural College, and 
Collaborator, Bureau of Plant Industry. 



Issued November 21, 1911. 




WASHINGTON : 

GOVERNMENT PRINTING OFFICE. 

1911. 



M 2 ^ 



1*^ < 



BUREAU OF PLANT INDUSTRY. 



Chief of Bureau, Beverly T. Galloway. 
Assistant Chief of Bureau, William A. Taylor. 
Editor, J. E. Rockwell. 
Chief Clerk, James E. Jones. 



Cotton and Truck Disease and Sugar-Plant Investigations. 

scientific staff. 

W. A. Orton, Pathologist in Charge. 

H. A. Edson and J. B. Norton, Physiologists. 

W. W. Gilbert, L. L. Harter, H. B. Shaw, F. J. Pritchard, F. A. Wolf, and H. W. Wollenweber, Assist- 
ant Pathologists. 

C. F. Clark, G. F. Miles, Clara O. Jamieson, Ethel C. Field, W. B. Clark, and A. C. Lewis, Scientific 
Assistants. 

E. C. Rittue, Joseph F. Reed, J. Rosenhaum, and L. O. Watson, Assistants. 

217 
2 









LETTER OF TRANSMITTAL 



U. S. Department of Agriculture, 

Bureau of Plant Industry, 

Office of the Chief, 
Washington, D. C, April 10, 1911. 
Sir: I have the honor to transmit herewith and to recommend 
for publication as Bulletin No. 217 of the series of this Bureau a manu- 
script entitled "Root-Knot and Its Control," by Dr. Ernst A. Bessey, 
professor of botany, Michigan Agricultural College, formerly a plant 
pathologist in this Bureau and now a collaborator of the Bureau of 
Plant Industry. This bulletin presents the results and conclusions 
of studies made by the author while in the service of the Bureau. 

Root-knot, which is widespread through the warm temperate and 
tropical zones of the whole world, is especially prevalent in this 
country in the South, and, as the bulletin shows, it is present even in 
the cold parts of the Northern States. It is also a very serious dis- 
ease of greenhouse plants all over the country. Fortunately, it is 
almost exclusively confined to the lighter types of soils, causing little 
or no damage in stiff clays. Dr. Bessey has worked out under field 
conditions a practical method of holding the pest in check. The 
means of its control in greenhouses had already been worked out, 
so that the methods presented here for controlling the pest in green- 
houses offer little that is new. The list of plants susceptible to this 
disease is more complete than any previous list published, contain- 
ing more than double the names of any other list. 
Respectfully, 

Wm. A. Taylor, 
Acting Chief of Bureau. 
Hon. James Wilson, 

Secretary of Agriculture. 

217 3 



CONTENTS 



Page. 

Introduction 7 

Symptoms of root-knot 7 

History of root-knot 8 

Plants affected by root-knot 10 

Plants not affected by root-knot '. 21 

Cross-inoculation experiments 22 

Distribution of root-knot 23 

The causal parasite 25 

Egg 26 

Larva 27 

Adult female 32 

Male 34 

Overwintering 36 

Comparison with Heterodera schachtii 36 

Methods of spread 37 

Effect on the host 39 

Conditions favoring root-knot 41 

Soil 41 

Moisture 42 

Temperature 42 

Control of root-knot 44 

Greenhouses, seed beds, etc 44 

Live steam 44 

Fresh soil 45 

Formaldehyde 46 

Miscellaneous 48 

Control of root-knot in the field on perennial crops 48 

Chemicals 49 

Carbon bisulphid 49 

Potassium sulphocarbonate 50 

Formaldehyde 50 

Calcium carbid 51 

Other chemicals 51 

Fertilizers 52 

Flooding 52 

Control of root-knot in the field when no crop is present 53 

Chemicals 53 

Carbon bisulphid 53 

Formaldehyde 53 

Calcium carbid 54 

Potassium sulphocarbonate 54 

Ammonium sulphate 54 

Fertilizers 56 

Flooding 58 

Drying , 60 

217 

5 



b CONTENTS 

Control of root-knot — Continued. 

Control of root-knot in the field when no crop is present — Continued. Page. 

Trap crops 61 

Steam ." 63 

Fallow 64 

Nonsusceptible crops 65 

Recommendations for freeing a field from root-knot 69 

Breeding strains resistant to root-knot 71 

Summary 72 

Bibliography 76 

Description of plates 82 

Index 83 



ILLUSTRATIONS 



PLATES. 

Page. 
Plate I. Stages in the development of Heterodera radicicola (Greef) Mull., etc. 82 

II. Fig. 1 — Root-knot on sugar beet. Fig. 2— Root-knot on squash 82 

III. Fig. 1 — Root-knot on carrot. Fig. 2 — Root-knot on clover 82 

TEXT FIGURES. 

Fig. 1. Heterodera radicicola. Half-grown female (?) individual shortly 

before the final molt 28 

2. Anterior portion of same nematode shown in figure 1 29 

3 Larva of Heterodera radicicola 29 

217 



B. P. I.-667. 



ROOT-KNOT AND ITS CONTROL. 



INTRODUCTION. 

The disease of plants known as root-knot, beaded root-knot, root- 
gall, eelworm disease, big-root, and probably under other names has 
been present in the United States for many years and has caused 
losses whose extent can not be calculated. Although more abundant 
in the South, it is present, at least sporadically, in all but the most 
Northern or Northwestern States as an out-of-doors pest and is every- 
where distributed in greenhouses. 

SYMPTOMS OF ROOT-KNOT. 

The presence of root-knot becomes noticeable when the affected 
plants become dwarfed or begin to die, but it is often present and 
causing a great reduction in the crop yield without the grower's 
knowledge. Indeed, it is probable that greater actual loss occurs 
from the form of the disease where, to the untrained eye, no signs are 
visible than in the case where the plants are actually killed, for a 
farmer soon learns by experience not to plant in infected regions those 
crops liable to total destruction, while he fails to notice a reduction in 
yield, especially if the disease be well established and not a recent 
introduction, so long as the affected plants do not show too great 
dwarfing or discoloration. 

Aside from the killing or dwarfing of the plants in severe cases 
or the reduction of yield in less serious infections there are no very 
noticeable symptoms apparent on those parts of the plant above 
ground. If rainfall has been rather scanty during the summer, the 
affected plants first show the lack of sufficient water, while sometimes 
the wilting is apparent when the sun is hot, even with abundant soil 
moisture. Occasionally no discoloration is noticeable, but usually 
plants that are badly affected show a lighter shade of green than un- 
affected plants. Since, however, the disease usually occupies large 
areas when it has been long established, there would be no opportunity 
ordinarily to compare affected with unaffected plants in mass, so that 
this difference would be readily overlooked. 

On the roots, on the contrary, very marked structural changes 
are apparent. Instead of being smooth and of uniform or slowly 

217 

7 



8 ROOT-KNOT AND ITS CONTROL. 

decreasing diameter toward the tip, they show irregular enlargements 
which involve the whole root if it be small or sometimes only one side 
of a large root. (Pis. II and III.) These are not superficial swell- 
ings only slightly attached to the root, as in the case of the bacterial 
tubercles of leguminous plants, but are integral parts of the root itself. 
On small roots these swellings may vary from only slightly greater 
than the thickness of the root to twice as thick, and spherical to spindle 
shaped; on larger roots they are usually lateral, or in bad cases may 
involve all sides, making a gall many times the normal diameter of 
the root and covered with furrows and seams until the root loses all 
semblance of its normal appearance. Such compound knots may 
reach a diameter of 3 or, rarely, even more centimeters and a length 
many times as great. 

HISTORY OF ROOT-KNOT. 1 

Root-knot has been known for many years both in the United 
States and abroad. It was apparently first mentioned in print by the 
famous mycologist Rev. M. J. Berkeley, 2 who described and figured 
roots of plants affected by this disease and recognized the animal na- 
ture of the organism causing it. The galls were observed by Greef on 
grass roots in 1864, but it was not until 1872 that the parasite received 
a name, 3 Anguillula radicicola Greef, after it had been observed sev- 
eral times on a number of different plants. In 1879 Cornu described 
this species, observed by him on sainfoin in 1874, as A. marioni. In 
1882 and 1885 the well-known plant pathologist, Prof. A. B. Frank, 
described it as a serious enemy of a number of cultivated plants in 
Germany. In 1883 and 1884 C. Muller made a careful study of the 
organism causing the disease and placed it in the genus Heterodera 
under the name of Heterodera radicicola (Greef) Muller. He showed 
it to be a close relative of the destructive sugar-beet nematode Hete- 
rodera schachtii Schmidt, w T hich has caused so much injury to the beet- 
sugar industry in Europe and which the writer found in 1907 in 
scattered localities in the United States. Treub in 1885 described as 
a parasite of sugar cane in Java what he considered to be a new 
species, naming it Heterodera javanica. This is considered now by 
most authors to be a synonym of H. radicicola. 

In the United States the root-knot early attracted the attention of 
greenhouse men as a serious pest of roses, violets, and other plants. 
J. N. May states 4 that he saw the disease, which he calls "club-root," 
on violets in 1876. We find the florists' papers full of references to 

i The full titles of all papers mentioned in this bulletin will be found in the "Bibliography," pp. 76-81. 
The a, b, c following a date, if given, refer to the first, second, and third papers published if more than one 
paper in that year is referred to. 

2 Berkeley, 1855. 

3 Greef, 1804 and 1872. 
« May, 1888. 

217 






HISTORY OF ROOT-KNOT. 9 

this trouble in the late eighties and early nineties. The first extensive 
investigation in this country was undertaken by Dr. J. C. Neal, 1 
of the Florida Agricultural Experiment Station, for the Division of 
Entomology of the United States Department of Agriculture. Owing 
to lack of access to literature he did not identify it with the pest 
previously described in Europe, but gave it the name Anguillula 
arenaria. Dr. N. A. Cobb, 2 then of New South Wales, in the absence 
of specimens from America, provisionally accepted Neal's species 
as distinct from the European species, renaming the former 
Tylenchus arenarius and the latter T. radicicola. He described the 
injury caused by it in New South Wales, and gave recommenda- 
tions as to treatment. In 1889 Prof. G. F. Atkinson, then connected 
with the Alabama Polytechnic Institute, at Auburn, Ala., described 
the disease, paying special attention to the life history of the parasite, 
which he correctly identified with the European species. In 1898 
Stone and Smith, of the Hatch Agricultural Experiment Station, 
published the most complete account yet written of the treatment 
of the trouble in greenhouses, at the same time giving some excellent 
illustrations of the parasite in various stages of development. 

In 1892 Goldi described a nematode parasitic on the roots of coffee 
in Brazil under the name Meloidogyne exigua. This proved subse- 
quently to be identical with Heterodera radicicola. Finally, in 1901, 
Lavergne, evidently misled by an erroneous statement as to the 
dimensions of Heterodera radicicola, described tins species from Chile 
as Anguillula vialae. 

The foregoing is by no means a complete list of the publications 
on the subject but embraces the papers that bear on the question 
of its synonymy and its occurrence in this country. 

The synonymy of the causal parasite is, then, as follows: 

Heterodera radicicola (Greef) Miiller, 1883. 
Syn. Anguillula radicicola Greef, 1872. 
marioni Cornu, 1879. 
arenaria Neal, 1889. 
vialae Lavergne, 1901. 
Heterodera javanica Treub, 1885. (?) 
Tylenchus arenarius Cobb, 1890. 
radicicola Cobb, 1890. 
Meloidogyne exigua Goldi, 1892. 

The writer's investigations of the subject were begun in 1900, 
but were soon interrupted for a period of years. Not until 1905 
was the work resumed in earnest and pursued with various inter- 
ruptions until its completion. The work was clone partly at Washing- 
ton, D. C, but mainly at Miami, Fla., at the Subtropical Laboratory 
and Garden of the Bureau of Plant Industry, and at Monetta, S. C, 

i Neal, 1889. 2 Cobb, 1890. 

217 



10 ROOT-KNOT AND ITS CONTROL. 

the majority of the field experiments being made at the last-named 
place. In addition to this, trips were made to the various parts of 
the country where the disease occurs or was suspected to occur. 
The caring for the experimental plats at Monetta, as well as the 
making of many of the observations on these experiments, was 
performed by Mr. J. M. Johnson, without whose services much of 
the writer's work would have been impossible. At Miami the 
cooperation of Mr. P. J. Wester, at that time gardener of the Sub- 
tropical Laboratory and Garden, was also of considerable assistance, 
although the experiments there were not on so large a scale as at 
Monetta. 

PLANTS AFFECTED BY ROOT-KNOT. 

The nematode causing root-knot seems to be one of the most 
omnivorous known. Neal, in 1889, reported about 65 species of 
plants as more or less subject to attacks by this pest. Reports by 
other investigators in different parts of the world and extensive 
experiments and observations by the writer have increased this 
number to 480 species and subspecies. Of this total number the 
writer has personally observed it on 291. The most complete list 
hitherto is that of Dr. Kati Marcinowski, 1 who lists 235 species 
(after subtracting hosts reported under two names). Almost all of 
the more important families of flowering plants are present in the 
list, as well as one gymnosperm and a fern. The plants include 
monocotyledons and dicotyledons, herbs and woody plants, annuals 
and perennials. Most of the garden plants are affected, as are many 
field crops. 

The list of plants shown in Table I is sure to be largely added to as 
investigations of this disease are carried on, and is not to be looked 
on as being in any way final. It is true that the writer has made 
many hundred examinations of plants in badly infested soil that did 
not take the disease, but such a list is of far less value than that of 
plants known to be susceptible. In the list are given (1) the scientific 
name of the plant; 2 (2) in parenthesis, the name under which it was 
reported, if different from the name now used ; (3) the common English 
name, if any; (4) the name of the person first reporting it on that host; 
(5) the date of observation; and (6) the degree of injury. Where the 
disease is reported on the host for apparently the first time, the name 
of the first observer is omitted, the observation having been made 
by the writer. In all cases where the writer has seen the plant 

i Marcinowski, Kati, 1909. 

2 The nomenclature followed is that used by the systematic botanists of the Bureau of Plant Industry. 
The list was submitted to the Office of Taxonomic Investigations of that Bureau, where it was revised by 
Mr. Homer C. Skeels. In a number of cases it would have been impossible, without seeing specimens, to 
determine to which of several segregates of a species the plant listed might belong, and in that case the 
original species name was retained, if still valid. 
217 



PLANTS AFFECTED BY ROOT-KNOT. 



11 



affected, whether previously reported or not, the name in the first 
column is preceded by an asterisk (*). In the last column the letters 
indicate the degree of injury only on those plants observed by the 
writer, the severest injury observed being reported, even though less 
severe cases have been observed — a = severe injury; b = nematodes 
abundant, but injury apparently not great; c = nematodes not abun- 
dant and no injury observed. It must be understood that under 
different circumstances many plants marked "a" would show little 
injury, while plants observed as uninjured and noted as "c" might 
easily be severely harmed under different conditions. Too much 
dependence can not, therefore, be laid on this column. In a number 
of cases the writer has grown in very badly infested fields plants 
reported by others as susceptible to root-knot, without the slightest 
signs of infection. Such cases are indicated in the list by a dagger (f). 
Some of these cases may be of species that are susceptible only under 
special conditions, while others may be due to erroneous observation 
on the part of the first observer or perhaps to the confusion of the 
bacterial root tubercle with the nematode gall. The former surmise 
may explain why the writer during a three years' residence in a part 
of Florida where the disease is very abundant failed to find it in any 
species of Citrus. Dr. H. J. Webber and Prof. P. H. Rolfs, who have 
studied plant diseases in Florida for many years, confirm this. Yet 
Dr. J. C. Neal * reports it as occurring on lemon, orange, and bitter- 
sweet orange, while a similar report is made by Lavergne from Chile. 2 
In the list those names added on the authority of Marcinowski 3 
are indicated by a double dagger (J) before the name of the plant. 

Table I. — List of plants susceptible to root-knot. 

[An asterisk (*) is used to show those plants which the writer has found affected with root-knot, and a 
dagger (t) those which he has grown in infested fields without infection, while a double dagger (J) shows 
the names of susceptible plants added on the authority of Marcinowski. In the last column a= severe 
injury; b, nematodes abundant, but injury apparently not great; c, nematodes not abundant and no 
injury observed.] 



Name of plant. 



Name of observer. 



Date of 
observa- 
tion. 



Charac- 
ter of 
injury. 



*Abelmoschus esculentus (L) Moench. Okra 

*Abronia augusta L. f 

*Abrus precatorius L. Paternoster bean , 

*Abutilon avicennae Gaertn. Chinese hemp 

Abutilon sp , 

* Acacia dealbata Link 

Acacia, several species from Australia. Wat- 
tle. 

Achyranthes sp 

Ageratum conyzoides L 

Ageratum sp 

Agropyron repens (L) Beauv. ( Triticum repens). 
Quack-grass. 



Neal. 



Atkinson. 



C. P. Lounsbury' 



Neal 

Breda de Haan. 
Zimmermann .. 
Greef 



1889 



1889 



i Neal, 1889. 
217 



2 Lavergne, 1901. 



3 Marcinowski, 1909. 



1908 

1889 

1899 

1900-1 

1872 

* In letter. 



12 ROOT-KNOT AND ITS CONTROL. 

Table I. — List of plants susceptible to root-knot — Continued. 



Name of plant. 



Name of observer. 



Date of 
observa- 
tion. 



Charac- 
ter of 
injury. 



Ajuga reptans L 

Alliaria officinalis Andrz. {Erysim u m alliaria I . 

* Allium ascalonicum L. Shallot 

* Allium cepa L. Onion 

* Allium fistulosum L. Welsh onion 

* Allium porrum L. Leek 

* Althaea rosea (L) Cav. Hollyhock 

*Amaranthus atropurpureus Roxb 

*Amaranthus caudatus L. Love-lies-bleeding. . 
*Amaranthus graecizans L. (A. albus). Tum- 

bleweed. 

*Amaranthus hybridus L. Slender pigweed 

*Amaranthus hybridus forma hypochondriacus 

(L.) Rob. Prince's feather. 

*Amaranthus palmcri S . Wats 

Amaranthus retroflexus L 

*Amaranthus spinosus L. Spiny amaranth 

* Amaranthus tricolor L 

*Ammi copticum L 

Amygdalus communis L. (Prunus communis). 
Almond. 

* Amygdalus persica L. Peach 

* Ananas sativus Schult. f. Pineapple 

Andropogon schoenanthus L 

Anemone apennina L 

*Anethum graveolens L. Dill 

Angelica archangelica L 

Angelica sylvestris L 

* Angelonia gardneri Hook 

*Anthemis cotula L. Mayweed 

* Antirrhinum majus L. Snapdragon 

*Apium graveolens L. Celery 

\Arachis hypogaea L. Peanut 

Arctium sp. Burdock 

*Argyreia nervosa (Burm.) Bojer 

Aristolochia clematitis L 

* Arrhenatherum elatius (L.) Beauv. Tall 

meadow oat-grass. 
% Artemisia absinthium L 

Artemisia caudata Michx 

Asclepias sp. Milkweed 

* Asparagus officinalis L. Asparagus 

Aster sp 

XAstrantia carniolica Wulf 

%Astrantia major L 

*Atriplex semibaccata- R. Br. Australian salt- 
bush. 

*Avena sativa L. Oats 

*Basella rubra L. Heart-leaved basel 

Begonia coccinea Hooker. (B. rubra) 

Begonia metallica L. Smith 

Begonia olbia Kuntze. (B. olvia) 

Begonia rex Putz 

*Bellis perennis L. Daisy 

*Benincasa cerifera Savi. Wax gourd 

Berberis vulgaris L. Barberry 

*Beta vulgaris L. Beet 

Bihai pulverulenta (Lindl.) Kuntze. (Helico- 
nia pulverulenta) . 

217 



Trotter. 
Trotter. 



1905-1 

1905-1 



Atkinson. 
Neal 



1889 
1889 



Neal. 



.do. 



1889. 
1889 



Breda de Haan . 
Trotter 



1899 
1905-1 



Licopoli. 
....do.. 



1877 
1877 



Janse . 
Neal. 
Selbv. 



1892 
1889 
1896 



Frank . 



1896 



Cobb . 
Neal. . 
Frank. 



1901 

1889 
1896 



Stursis 

Dalla Torre. 
do 



]893 
1892 
1892 



Halsted . 



1891 



Selbv. . . 

do.. 

do.. 

Molliard . 



1896 
1896 
1896 
1900 



Frank.. 
....do. 

Ross... 



1885 
1885 
1883 



PLANTS AFFECTED BY ROOT-KNOT. 13 

Table I. — List of plants susceptible to root-knot — -Continued. 



Name of plant. 



*Boerhaavia decumbens Vahl 

*Boerhaavia erecta L 

Bosea amherstiana (Moq.) Hook. f. (Rodetia) 
*Boussingaultia basselloides H. B. K. 



Madeira 



%Bouvardia sp . 

*Brassica campestris L. Rutabaga 

*Brassica juncea (L.) Cass. Chinese mustard. . . 

*Brassica napus L. Rape 

*Brassica nigra L. Mustard 

*Brassica oleracea botrytis L. Cauliflower, broc- 
coli. 

*Brassica oleracea capitata L. Cabbage 

*Brassica oleracea viridis L. Kale, collard . . . . . 

*Brassica pekinensis (Lour.) Skeels. Chinese 
cabbage. 

*Brassica rapa L. Turnip 

Buddleia sp 

Bursa bursa-pastoris (L.) Britt. (Capsella 
bursa-pastoris) . Shepherd's purse. 

*Cajan indicum Spreng. Pigeon pea 

Cananga odorata (Lam.) Hook, and Thorn. 
Ylang-ylang. 

*Canavali ensiforme (L.) DC. Jack bean 

*Capriola dactylon (L.) Kuntze. Bermuda 



^Capsicum annuum L. (including C. cordiforme I . 

Red pepper. 
* Cardiospermum halicacabum L. Balloon vine. 
*Carica papaya L. Papaya or melon pawpaw. . 
*Carissa bispinosa (L.) Desf 

Carpinus betulus L. Beech 

*Carthamus tinctorius L. Safflower 

*Carum carvi L. Caraway 

Cassia mimosoides L 

^Cassia tora L. (C. obtusifolia) . Wild senna, 
coffee bean. 

Castanea sativa Miller (C.vesca). Chestnut. 

*Catalpa speciosa Warder. Catalpa 

*Cecropia palmata Willd 

* Centaur ea cyanus L . Cornflower 

Centratherum reticulatum (DC.) Benth 

*Ceratonia siliqua L. Carob or St. -John 's- 

bread. 
* Chaetochloa italica (L.) Scrib. German millet 

* Chenopodium album L. Lamb's quarters 

*Chenopodiurn anthelminthicum L. Wormwood 

* Chenopodium boscianum Moq 

Chenopodium botrys L. Jerusalem oak 

* Chenopodium sp. (Not any of the preceding) . 
Chrysanthemum cinerariaefolium (Trev.) Vis. . 

\Chrysanthemum leucanthemum L. Oxeye 
daisy. 

* Chrysanthemum ep. Chrysanthemum 

*Cicer arietinum L. Chick-pea 

*Cichorium endivia L. Endive 

Cichorium intybus L. Chicory 

Cinchona sp. Peruvian bark 

i In letter. 
217 



Name of observer. 



Trotter. 
Neal . . 



Mosseri . . 
Atkinson. 



Date of 
observa- 
tion. 



1905-2 
1889 

1903 
1889 



Neal. 



.do. 



Atkinson. 

Neal 

do... 



Breda de Haan . 
Mosseri 



Neal. 



Trotter. 



Frank 

G. A. Gammie 1 
Atkinson 



Trotter. 



G. A. Gammie 



Charac- 
ter of 
injury. 



1889 
1889 



1889 
1889 
1889 



1899 

1903 

1889 



1905-1 



1885 
1908 
1889 

1905-2 



1908 



Atkinson. 



Neal. 



Gvozdenovic 

Darboux and Hou- 
ard. 



Kamerling. 
Licopoli... 
Barber 



1889 



1889 



1902 
1901 



1903 
1877 
1901 



14 ROOT-KNOT AND ITS CONTROL.. 

Table I. — List of plants susceptible to root-knot — Continued. 



Name of plant. 



Name of observer. 



Date of 
observa- 
tion. 



Charac- 
ter of 
injury. 



Circaea intermedia Ehrh 

Circaea lutetiana L. Enchanter's nightshade. 
*Citrullus vulgaris Schrad. Watermelon. .. 

Citrus aurantium L. (C. vulgaris). Bitter 
orange. 

Citrus aurantium sinensis L. (C aurantium). 
Sweet orange. 

Citrus limonum Risso. Lemon 

%Clematis florida Thunb 

j Clematis hybrida Hort 

XClematis lanuginosa Lindl. and Paxt 

* Clematis paniculata Thunb 

% Clematis patens Morr . and Decais 

Clematis vitalba L 

XClematis viticella L 

Clematis sp 

*Coffea arabica L. Coffee 

Coffca liberica Hiern. Liberian coffee 

Coffea robusta Hort. Robusta coffee 

Coleus blumeiBenth. (C.verschaffelti). Coleus. 

Coleus scutellarioides (L.) Benth. Coleus 

Coleus sp. (Coleus var. sp.). Coleus 

*Corchorus olitorius L. Jute 

*Coriandrum sativum L. Coriander 

*Coronopus procumbens Gilib 

Corylus avellana L. Filbert 

* Cosmos bipinnatus Cav. Cosmos 

Crepis leontodontoides Allioni. Hawk's- 

beard. 
XCrepis pulchra L 



Tischler. 
....do.. 
Neal.... 
....do.. 



.do. 



....do. 

Chifflot 
....do. 
....do. 



1902 
1902 
1889 
1889 

1889 

1889 
1900 
1900 
1900 



Chifflot 

Cornu 

Chifflot 

Muller 

Jobert 

Bouquet de la Grye. 

Cramer 

Frank 

Breda de Haan 

Neal 



1900 
1879-2 
1900 
1884 
1878 
1899 
1906 
1885 
1905 
1889 



Casali. 



1898 



Trotter. 



* Crotalaria juncea L . Sunn hemp , 

*Croton glandulosus simpsonii Ferg 

*Cucumis melo L. Muskmelon 

*Cucumis sativus L. Cucumber 

*Cucurbita maxima Duch. Squash 

*Cucurbita moschata Duch. Squash 

*Cucurbita pepo L. Pumpkin, squash 

Cuminum cyminum L. Cumin 

*Cyamopsis tetragonoloba (L.) Taub. Guar... 
X Cyclamen europaeum L . Cyclamen 

Cyclamen persicum Mill. Cyclamen 

*Cydonia oblonga Mill. Quince 

*Cyperus esculentus L. Chufa 

*Dactylis glomerata L. Orchard grass 

Dahlia pinnata Cav. (D. variabilis). Dahlia. . 

Datisca cannabina L 

*Daucus carota L. Carrot , 

Desmodium sp 

*Deutzia crenata S. and Z. Deutzia 

*Dianthus barbatus L. Sweet William 



Darboux and Hou- 
ard. 



1905-1 
1901 



Neal 

Berkeley. 



Frank. 



Pink. 



*Dianthus caryophyllus L. Carnation. 

*Dianthus chinensis heddewiqi Regel. 

*Dianthus plumarius L. Pink 

XDieffenbachia sp , 

XDioscorea illustrata Hort. Yam 

*Diospyros kaki L. f. Japanese persimmon. 
*Diospyros vir"iniana L. Persimmon 



Peglion 

Osterwalder. 



Neal 

Trotter.. 
Licopoli. 
Barber. . 



fTre lease. 
\? Lotey.. 



Schlechtendal. 
Queva 



1889 
1855 



1885 



1902 
1901 



1889 
1902 
1877 
1901 



1894 
1892 



1886 
1895 



217 



PLANTS AFFECTED BY ROOT-KNOT. 
Table I. — List of plants susceptible to root-knot— Continued. 



15 



Name of plant. 



Dipsacus fullonum L. Teasel 

%Dipsacus sylvestris Huds 

Dodartia orientalis L 

*Dolicholus intermedins (T. and G.) Vail 

*Dolichos bifiorus L 

*Dolichos lablab L. Hyacinth bean or Bona- 

vist bean. 
*Dolichos umbellatus Thunb 

Dracaena rosea Hort. Dragon tree 

*Eclipta alba (L.) Hask 

XEleocharis palustris (L.) R. Br 

*Eleusine coracana (L.) Gaertn. Ragi millet. . . 

*Eleusine indica (L.) Gaertn. Wire-grass 

*Elichrysum bracteatum (Vent.) Andr. Im- 
mortelle. 

Elymus arenarius L. Downy lyme-grass 

*Emilia sagittata (Vahl.) DC. Scarlet tassel 
flower. 

*Eruca sativa Mill. Roquette 

*Erythrina americana Mill. Coral tree 

Erythrina cristagalli L 

*Eschscholtzia californica Cham. California 
poppy. 

Eupatorium capillifolium. (Lam.) Small. 
(E. foeniculaceum). 

Euphorbia cyparissias L. Cypress spurge 

^Euphorbia nutans Lag 

Euphorbia peplis L. Leafy spurge 

*E)iphorbia pilulifera L 

*Fagopyrum vulgare Hill. Buckwheat 

*Festuca elatior L. Meadow fescue 

*Festuca ovina L. Sheep fescue 

*Ficus aurea Nutt. Strangling fig. Wild 
rubber plant. 

*Ficus carica L. Fig 

*Ficus elastica Roxb. Rubber plant 

*Ficus sp. 2 (from Natal) 

*Ficus sp. 2 (from Mexico) 

Filicinae, genus and species not stated. Fern 

*Foeniculum vulgare Hill. Sweet fennel 

*Fragaria chiloensis (L.) Duches. American 
strawberry. 

Fragaria vesca L. European strawberry 

t Fuchsia sp. Fuchsia 

Galinsoga parviflora Cav 

*Gardenia jasminoides Ellis (G . florida) . Cape 
jasmine. 

^Gladiolus sp. Gladiolus 

*Glycinehispida (Moench) Maxim. (Sojabean.) 

Soy bean. 
*Gossypium barbadense L. Sea Island cotton. 

*Gossypiu7n hirsutum L. Upland cotton 

*Grabowskia glauca Hort 

* Hardenbergia monophylla (Vent.) Benth. 

Australian sarsaparilla. 
*Hedysarum coronarium L. Sulla 

Helianthus annuus L. Sunflower 

*Helianthus debilis Nutt. Sunflower 

^Helianthus tuberosus L. Jerusalem artichoke 



Name of observer. 



Frank 

Hieronvmus. 
Greef 



Frank 

Lagerheim. 



Warmins 



Licopoli. 



Neal. 



Licopoli. 



Date of 

observa- 
tion. 



1885 
1890 

1872 



1885 



1905 



1877 



1877 



1889 
1877 



Trotter. 



Neal. 



Stone and Smith. 



Trotter.. 
Mosseri . 
Tarnani. 
Neal.... 



Frank. 
Neal.. 



.do. 



Neal. 



1905-1 



1889 



1898 



Charac- 
ter of 
injury. 



1905-1 
1903 
1898 
1889 



1882 

1889 
1889 



1889 



i According to Ritzema Bos (1900-1) this injury is due to another nematode, Tylenchus hordei. 
- Species distinct from the preceding. 

91294°— Bui. 217—11 2 



16 BOOT-KNOT AND ITS CONTROL. 

Table I. — List of plants susceptible to root-knot — Continued. 



Name of plant. 



Heliotropium sp. Heliotrope 

* Heteropteris sp 

Hibiscus coccineus Walt. Rose mallow 

* Hibiscus 7'osa-sinensis L. Hibiscus 

* Hibiscus sabdariffa L. Roselle 

* Hibiscus syriacus L. Rose of Sharon 

*Hicoria pecan (Marsh) Britt. Pecan 

Hordeum sativum. Barley 

Hypericum perforatum L. St.-John's-wort. . . 

Hyssopus sp. Hyssop 

Iberis umbellata L. Candytuft 

*Ilysanthes dubia (L.) Barnh 

Impatiens balsamina L. (Balsamina hortensis). 

Balsam. 
Impatiens kleinii Wight and Arn 

* Ipomoea batatas (L.) Poir. Sweet potato 

Ipomoea bona-nox L. Moonflower 

* Ipomoea cathartica Poir. Wild morning-glory. 

* Ipomoea fuchsioides Griseb. Fuchsia-flowered 

morning-glory. 
Ipomoea lacunosa L 

* Ipomoea purpurea L. Roth. Morning-glory . . . 

* Ipomoea quamoclit L. Cypress vine 

*Ipomoea setosa Ker 

*Ipomoea syringaefolia Meissn. Tree morning- 
glory. 

*Ipomoea sp. 2 Indian potato 

*Iresine paniculata (L.) Kuntze 

Iris sp. Iris 

Ixora aurea Hort 

Ixora chinensis Lam. {Ixora fiammea) 

Ixora crocea Hort 

%Ixora fraseri Hort - 



(Ipo- 



Ixora sp. 2 

Jacquemontia tamni/olia (L.) Griseb. 

moea tamni/olia.) 
Juglans cinerea L. Butternut 

* Juglans regia L. Persian (English) walnut... 

* Juglans rupestris Engelm. Arizona walnut... 
\Juncus gerardi Loisel 

Kadsura sp. ( Cadsura) 

*Konig maritima (L.) R. Br. Sweet alyssum.. 
*Kraunhia sinensis (Sims) Greene. Wistaria. . . 

*Lactuca sativa L. Lettuce 

*Lagenaria vulgaris Ser. Gourd 

*Lamium amplexicaule L. Dead nettle 

Lantana horrida H. B. K. Lantana 

*Lathyrus cicera L. Lesser chick-pea 

*Lathyrus odoratus L. Sweet pea 

*Lathyrus sativus L. Bitter vetch 

*Lathyrus tingitanus L. Tangier pea 

*Lens esculenta Moench. Lentil 

Leontodon hastilis L. Hawkbit 

%Lepidium sativum L. Garden peppergrass 

*Lespedeza bicolor Turcz. Bush clover 

■\Lespedeza striata (Thunb.) Hook. Japan 
clover. 



Name of observer. 



Stone and Smith. 



Neal. 



Neal... 

do. 

Trotter. 

do. 

Frank.. 
Neal... 



Frank. 



G. A. Gammie 



Stone and Smith. 



Atkinson. 

Neal 

....do... 



Brick 

f 1 ornu 

....do 

do 

Darboux and Hou- 
ard. 

Cornu 

Atkinson 



Neal. 



.do. 



Lagerheim 

Breda de Haan. 



Frank. 
Neal.. 



J. J. Thornber '. 



Frank. 
Voigt. 



Atkinson. 



Date of 
observa- 
tion. 



1898 
'l889' 



ISS!) 
1889 
1905-1 
1905-1 
1896 
1889 



1885 
1908 

i898' 



1889 
1889 
1889 



1905 
1879-1 
1879-1 
1879-1 

1901 

1879-1 

1889 

1889 
1889 



1905 
1899 



1882 
1889 



1907 



1885 
1890 



1889 



217 



1 In letter. 



2 Species distinct from the preceding. 



PLANTS AFFECTED BY ROOT-KNOT. 17 

Table I. — List of plants susceptible to root-knot — Continued. 



Name of plant. 



Name of observer. 



Date of 
observa- 
tion. 



Charac- 
ter of 
injury. 



*Ligustrum ovalifolium Hassk. California 
privet. 

*Linaria canadensis (L.) Dumont. Toadflax 

Linum angusti [folium Huds 

*Linum usitatissimum L. Flax 

*Lippia nodiflora (L.) Michx. Frog-fruit 

* Lobelia erinus L 

*Lonicera japonica Thunb. Japanese honey- 
suckle. 

* Lotus corniculatus L. Bird's-foot trefoil 

Lotus sp. 

*Leucacna glauca (L.) Benth 

*Lucuma rivicoa anguslifolia Miq. Ty-ess 

*Luffa cylindrica (L.) Roem. Sponge gourd. . . 

*Lupinus alb us L. White lupine 

*Lupinus angustifolius L 

*Lupinus luteus L. Yellow lupine 

*Lupinus termis Forsk 

* Lycopersicon csculentum Mill. Tomato 

Mains sylvestris Mill. (Pyrus malus). Apple. . 
"Malia rotundifolia borcalis (Wallm.) Masters. 
W T ild mallow. 

* Manihot utilissima Pohl. Cassava 

* Marrubium vulgare L. Horehound 

* Mcdicago saliva L. Alfalfa, or lucern 

f Meibomia mollis ( Vahl) Kuntze. Florida beg- 

garweed. 

* Meibomia strict a (Pursh) Kuntze 

* Melia azedarach L. Umbrella tree 

*Mclilotus alba Desr. White sweet clover, or 

Bokhara clover. 
*Melilotus indica (L.) All 

* Melothria crassifolia Small 

Mesembryanthemum sp. Fig marigold 

Modiola caroliniana (L.) Don. (M. multifida).. 
Mollugo pentaphylla L. ( M. stricta) 

*Mollugo verticillata L. Carpet weed 

* Momordica charantia L . Balsam apple 

*Morus alba multicaulis (Perr.) Loud. Mul- 
berry. 

*Morus alba tatanca (L.) Loud. Mulberry 

* Moms nigra L. Mulberry 

* Moms rubra L. Mulberry 

Mulgediummacrophyllum (Willd.) DC 

Musa cavendishii Lamb. (Musa chinensis). 

Dwarf banana. 

*Musa e.tsete Gmel. Brace's banana 

Musa paradisiaca dacca (Horan) Baker (M. 

dacca). Dacca banana. 
Musa paradisiaca sapientum (L.) Kuntze. 
Banana. 

Musa rosacea Jacq 

*Musa texiilis Nee. Manila hemp 

*Nicotiana sanderae Hort 

*Nicotiana tabacum L. Tobacco 

Nolana sp 

*Ocimum basilicum L. Basil 

Oldenlandia sp 

Onobrychis viciaefolia Scop. Sainfoin 



Trotter. 
Sorauer . 



1905-1 
190(3 



Atkinson . 
Trotter... 



1889 
1905-2 



Neal.. 
Selby. 



1889 
1896 



Neal 

Atkinson. 

Frank 

Rolfs.... 



1889 

1889 
1882 
1898 



Atkinson . 



1889 



Neal 

Atkinson 

G. A. Gammie 1 . 



1889 
1889 
1908 



Miiller. 
Ross. .. 



1884 
1883 



Ross 

Delacroix. 
Miiller 



1883 
1904 

1884 



J&nse 

NV ; ,1 

Breda de llaan. 
G. A. Gammie 1 
Cornu 



1892-2 

1889-1 

1899 

1908 

1879-2 



217 



i In letter. 



18 liOOT-KNOT AND ITS CONTROL. 

Table I. — List of plants susceptible to root-knot — Continued. 



Name of plant. 



*Ornithopus sativus Brot. Seradella 

*Oxalis corniculata L. Sheep sorrel 

Oxalis stricta L 

*Paeonia sp. Peony 

*Paliurus spina-Christi Mill. Christ's-thorn 

*Panax quinquefolium L. Ginseng 

Papaver rhot us L. Poppy 

Papyrius papyri/era (L. ) Kuntze (Broussonettia 
papyrifcra). Paper mulberry. 

*Passifiora incarnata L. Passion flower 

*Passiflora pfordli ( = X-P. alato-caerulea'L\\\i\\ . | 

Passiflora sp 

*Pastinaca sativa L. Parsnip 

^Pelargonium zonale (L.) Ait. Geranium 

*Pentagonia physalodcs (L.) Hiern 

*Perillafrutesccns (L.) Britt. Perilla 

^Persca gratissima Gaertn. f . Avocado 

*Petroselinum sativum Hoffm. Parsley 

*Petunia hybrida Vilm. Petunia 

*Phaseolus aconitifolius Jacq. Aconite-leaved 

bean. 
*Phaseolus angularis (Willd.) Wight. Adsuki 
bean. 

*Phaseolus calcaratus Roxb. Seeta bean 

*Phaseolus lunatus L. Lima bean 

*Phaseolus max L. Green gram, or mung bean . 

*Phaseolus radiatus L. Green gram 

*Phaseolus rctusus Moench. Metcalfe bean . . . 
*Phaseolus vulgaris L. (incl. P. nanus). Bean. 

Physalis peruviana L. Cape gooseberry 

Physalis sp 

^Phytolacca americana L. (P. decandra). Poke- 
weed. 
*Pilea serpyllifolia (Poir) Wedd. Artillery 
plant. 

Piper betle L. Betel pepper 

Piper nigrum L. Pepper 

*Piriqueta tomentosa (Willd.) H. B. K 

*Pisum arvense L. Field pea 

*Pisum, sativum, L. Garden pea 

*Pithecolobium saman (Jacq.) Benth. Rain 
tree. 

Plantago lanceolata L. Rib-grass 

Plantago major L. Plantain 

* Plantago sp 2 

Platanus sp. Plane tree 

Plectranthus sp 

*Pluchea purpurascens (Swartz) DC 

* Plumbago capensis Thunb. Cape leadwort 

Poa annua L. Annual bluegrass 

%Poa pratensis L. Kentucky bluegrass 

Podranea ricasoliana (Tanf.) Sprague (Te- 
coma mackennii). 
*Polianthcs tubcrosa L. Tuberose 

Polygala oleifera Hort 

* Polygonum nydropiperoides Mich 

Polygonum sp 

*Portulaca grandiflora Hook. Portulaca 



Name of observer. 



Tarnani. 



Van Hook. 
Tarnani... 
Neal 



Magnus . . 
Atkinson. 



Laversne. 



Neal. 



Date of 
observa- 
tion. 



1 898 



1904 
1898 
1889 



1888 
1889 



1901 



1889 



Neal 

C. P. Lounebury '. 

Atkinson 

....do 



Zimmermann 

Delacroix 



Neal. 



Licopoli. 
Frank... 



Gandara. 
Frank... 



Greef 

Henning 

C. P. Lounsbury '. 



Breda de Haan. 
Tarnani 



1889 
1908 
1889 
1889 



1900-2 
1904 



1889 



1877 
1885 



1906 

1885 



1872 
1898 
1908 



1899 
is98' 



i In letter. 



- Species distinct from tbe preceding. 



217 



PLANTS AFFECTED BY ROOT-KNOT. 

Table I.— List of plants susceptible to root-knot — Continued. 



19 



Name of plant. 



*Portulaca oleracea L. Purslane 

%Primula auricula L. Primrose 

%Primula carniolica Jacq. Primrose 

Prunus armeniaca L. Apricot 

Prunus cerasifera Ehrh. (P myrobalanus) 

Prunus domestica L. Plum 

Prunus japonica Thunb. (P. nana and P. 
lanceolata), 

* Prunus virginiana L. Choke cherry 

*Prunus sp. 1 (from Mexico). Cherry 

*Psidium guajava L. Guava 

*Punica granatum L. Pomegranate 

Pyrus communis L. Pear 

Quercus suber. Cork oak 

*Radicula armoracia (L.) Robinson. Horse- 
radish. 

*Radicula walteri (Ell.) Greene 

*Raphanus sativus L. Radish 

* Reseda odorata L. Mignonette 

%Rhinanthus cristagalli L. Rattlebox 



%Ribes rubrum L. Currant . 

*Rosa chinensis manetti Dippel. Manetti rose. . 

*Rosa laevigataMichx. Cherokee rose 

*Rosa setigera Michx. Rose 

Rosa sp. Rose 

Rubusidaeus L. Raspberry 

Rubus subuniflorus Rydb . (R. villosus) . Black- 
berry. 

Rubus trivialis Mich 

*Rumex acetosa L. Sorrel 

*Rumex sp. 1 Dock 

*Saccharum officinarum L. Sugar cane 

Salix babylonica L. Weeping willow 

Salvia sp. Sage 

%Sanicula europaea L. Wood sanicle 

Scabiosa columbaria L 

Schizonotus sorbifolius (L.) Lindl. (Spiraeasor- 

bifolia). 
*Scolymus hispanicus L. Spanish oyster plant. 
*Scorzonera hispanica L. Black salsify 

Sedum (several species) 

Sempervivum glaucum Ten 

*Sem,pervivum tectorum L 

Senecio vulgaris L 

*Sesban bispinosa (Jacq.) Steud 

*Sesban maa'ocarpa Muhl 

Sesuvium maritimwn (Walt.) B. S. P. (S. pen- 
tandrum) . 

* Sesuvium portulacastrum L 

*Sida rhombifolia L 

*Sida spinosa L 

*Smilax glauca Walt 

*Solanum carolinense L. Horse nettle 

Solanum dulcamara L. Bittersweet 

* Solarium melongena L. Eggplant 

*Solanum nigrum L. Nightshade 

*Solanum rostratum Dun. Buffalo bur 

*Solanum tuberosum L. Potato 



Name of observer. 



Neal 

Dalla Torre. 

....do 

Neal 

....(In 

....do 

....do 



Frank 

Ducomet. 



Neal. 



Darboux and Hou- 

ard. 
Cobb 



Halsted. 
Selby... 
Neal.... 



.do. 



Breda de Haan. 

Neal 

Frank 

Cornu 

Sorauer 

Neal 



Greef . . . 
Licopoli . 
....do.. 
Trotter. . 



Neal. 



Atkinson. 



Mosseri. . 
Atkinson. 



Date of 
observa- 
tion. 



1889 
1892 
1892 
1889 
1389 
1889 
1889 



1882 
1908 



1889 
190i 
1901 



1891 
1896 
1889 

1889 



1899 
1899 
1896 
1879-2 
1906 
1889 



1872 

1877 

1875 

1905-1 



1889 



1889 



1903 
1889 



Neal. 



1889 



Charac- 
ter of 
injury. 



217 



i Species distinct from the preceding. 



20 ROOT-KNOT AND ITS CONTROL. 

Table I. — List of plants susceptible to root-knot — Continued. 



Name of plant. 



Name of observer. 



*Solanum sp. 1 

Sonchus arvensis L. Sow thistle 

Sonchus oleraceus L 

*Spergula arvensis L. Spurry 

Spermadictyon suaveolens Roxb. (Hamiltonia 
spectabilis) . 
*Spinacia oleracea L . Spinach 

* Spiraea cantoniensis Lour. Spiraea 

*Spondias lutea L. Hog plum 

%Stephanotis sp 

*Stizolobium pachylobium . Piper and Tracy. . 

■\Stizolobium pruriens (L.) Medic 

jStizolobium deeringianum Bort ( Mucuna utilis). 

Velvet bean. 
Strelitzia nicolai Reg. and Koern. Bird-of- 

paradise flower. 
*Syncarpia glomiilifera (Sm.) Niedenz 

* Tamarindus indica L. Tamarind 

* Tanacetum vulgare L. Tansy 

Taraxacum, officinale Weber. Dandelion 

* Tetrapanax papyrifer (Hook.) Koch. Japanese 
paper plant. 

Thea sinensis L. Tea , 

J Theobroma cacao L. Chocolate or cacao 

Theophrasta crassipes Lindl 

* Thunbergia fragrans Roxb 

* Tragopogon porrifolius L. Salsify 

* Trichosanthes cucumeroides (Ser.) Maxim 

* Trifolium alexandrinum L. Egyptian clover, 

Berseem. 

* Trifolium incarnatum L. Crimson clover 

* Trifolium pratense L. Red clover 

* Trifolium repens L. White clover , 

* Trigonella foenum-graecum L. Fenugreek 

Triticum aestivum L. (T. sativum). Wheat. . . 
Triumfetta rhomboidea Jacq 

*Tropaeolum majus L. Nasturtium 

* Tropaeolum minus L. Dwarf nasturtium 

* Ulmus campestris L. European elm 

* Verbascum thapsus L. Mullein 

Verbesina occidentalis (L.) Walt. Crownbeard. . 

*Verbesina virginica L. (V. sinuata). Crown- 
beard. 

* Veronica peregrina L. Speedwell 

* Veronica tournefortii Gmelin 

X Viburnum lantana L. Wayfaring tree 

j Viburnum tinus L. Laurestine 

* Vicia atropurpurea Desf 

* Vicia faba L. Horse bean 

* Vicia fulgens Battand. Scarlet vetch 

* Vicia hirsuta (L.) S. F. Gray 

* Vicia monanthos (L.) Desf 

* Vicia narbonensis L. Narbonne vetch 

* Vicia pseudocracca Bertol 

* Vicia sativa L. Vetch 

* Vicia villosa Roth. Hairy vetch 

* Vigna repens Baker 



Tarnani. 
Frank... 



Comu. 



Voigt. 



Piper and Cobb '■ 
Rolfs 



Ross. 



Licopoli. 



Barber 

RitzemaBos. 
Comu 



Atkinson. 



Frank... 

do.. 

Sheldon. 



Sorauer 

G. A. Gammie 2 . 



Neal. 



.do. 



Date of 

observa- 
tion. 



1898 

1885 



1879-1 



1890 



1910 
1898 

1883 



1877 



1901 

1900 

1879-1 



1889 



1885 
1885 
1905 



1906 
1908 



1889 
1889 



Frank.. 
Kieffer. 



1896 
1901 



1 Species distinct from the preceding. 



2 In letter. 



217 



PLANTS NOT AFFECTED BY ROOT-KNOT. 
Table I. — List of plants susceptible to root-knot — Continued. 



21 



Name of plant. 



*Vigna unguiculata(L.) Walp. ( Vigna catjang, 
Dolichos catjang). Cowpea. 

* Viola odorata L. Violet 

Yitis aestivalis Michx. Grape 

Vitis labrusca L. Grape 

Viiis serianaefolia (Bunge) Maxim. (Cissus 

aconitifolia) . 

* Vitis vinifera L. Old World grape 

*Washingtonia filifera microsperma l Beeeari. 

California fan palm. 

*Washingtonia gracilis 1 Parish 

Willughbaea scandens (L.) Kuntze. (Mileania 

scandens) . 

*Zamia floridana DC 

\Zea mays L. Maize or Indian corn 



Name of observer. 



Neal. 



Halsted. 
Neal.... 
Licopoli. 
Cornu... 



Neal. 



Neal. 
Neal. 



Date of 
observa- 
tion. 



1889 

1891 

1889 

1877 

1879-2 

1899 



1899 
"1889* 



Charac- 
ter of 
injury. 



1 Seed received under this name from Dr. O. Beccari. 



PLANTS NOT AFFECTED BY ROOT-KNOT. 

Among the plants grown by the writer in infected land without 
their becoming infected with root-knot in the slightest degree were sev- 
eral species of Stizolobium, the genus to which the velvet bean belongs, 
viz, Stizolobium lyoni, S. pruriens, 8. hirsutum, and the velvet bean and 
one or more other unidentified species of this genus. 1 Many of the 
grasses seem to be resistant. Thus the writer has failed to find the 
nematode on crab-grass (Syntherisma sanguinalis), redtop (Agrostis 
alba), Johnson grass (Andropogon halepensis) , some varieties of oats 
(Avena sativa) — -but some are susceptible — Bromus schraderi, Eusta- 
chys petraea, some varieties of barley (Hordeum vulgar •e), Lolium 
perenne, Japanese barnyard millet (Echinochloa frumentacea) , broom- 
corn millet, or proso (Panicum miliaceum), pearl millet (Pennisetum 
sp.), timothy (Phleum pratense), rye (Secale cereale), the various forms 
of sorghums, milos, Kafir corn, etc. {Andropogon sorghum), wheat 
(Triticum aestivum), but see list of susceptible plants. The same is 
true of corn (maize, Zea mays) as of wheat. Euchlaena luxurians 
was also free. Several Composite seem to be free from the trouble 
even where the nematodes are very abundant in the soil. Thus, 
Bidens leucantha and B. bipinnata always were found free. Gna- 
phalium purpureum, Helenium tenuifolium, species of Solidago, Zinnia, 
etc., were also free. The absence of nematodes in the plants above 
enumerated is far less significant than their presence in other plants, 
for conditions may have been unfavorable, and yet under other con- 

i Rolfs, however, 1898, reports root-knot on the velvet bean, and recently Prof. C V. Piper has found it in 
abundance on plants of Stizolobium pruriens, S. P. I. 21566, grown in a greenhouse in Washington, D. C 
Evidently under certain conditions some strains may be susceptible, but as a rule it is immune. 
217 



22 ROOT-KNOT AND ITS CONTROL. 

ditions they might have shown root-knot. However, it is probable 
that the above-named plants will show themselves nematode resistant 
in most cases. 

CROSS-INOCULATION EXPERIMENTS. 

It has been suggested by several investigators that Heterodera 
radicicola, like Tylenchus dipsaci, may show the development of 
strains preferring certain hosts and exhibiting a reluctance to attack 
others, although these different strains are morphologically indis- 
tinguishable. 1 This explanation has been suggested for the fact 
recorded by Stone and Smith 2 that lettuce often is not attacked in 
beds in greenhouses where other crops suffer great injury. The 
writer accordingly made a number of cross-inoculation experiments 
to determine, if possible, to what extent the nematodes of certain 
generally grown crops were interchangeable. The experiments 
were performed as follows: Pots of soil were sterilized in an autoclave 
for about an hour and a half, sometimes longer, at a temperature of 
125° C. While this was perhaps not long enough to kill all bacterial 
spores in the center of the pots, the temperature attained showed 
itself to have been high enough to kill all nematode larvae or eggs. 
In the sterilized soil were placed affected roots of the plant used as a 
source of the nematodes. These roots were first carefully washed 
(sometimes in water containing a small amount of formaldehyde) to 
remove all adhering dirt in which conceivably larvre or eggs of other 
strains of nematodes might be present. These pots were planted with 
seeds of plants to be tested as possible hosts of the nematode, either 
at the same time or a few daj^s after the roots were put into the pots. 
Except when it was certain that the water v/as nematode free, it was 
boiled and cooled before using it to water the pots. Experiments 
made in this manner showed that the root-knot nematodes were 
mutually interchangeable in the following plants: Red clover ( Tri- 
folium pratense; PL III, fig. 2), white clover (T. repens), crimson 
clover (T. incarnatum), cowpea (Vigna unguiculata) , strawberry 
(Fragaria cMloensis), tree morning-glory (Ipomoea syringaefolia) , 
sunflower (Helianthus debilis), horse bean (Vicia faba), ginseng 
(Panax quinquefolium) , purslane (Portulaca oleracea) , fig (Ficus carica), 
papaya (Carica papaya), catalpa (Catalpa speciosa), tomato (Lyco- 
persicon esculentum) , and Old World grape (Vitis vinifera). These 
all also affect the following, for which the reverse inoculation experi- 
ments were not made: Lettuce (Lactuca sativa), green gram (PJiase- 
olus radiatus), tobacco (Nicotiana tabacum), squash (Cucurbita 
moschata), cucumber (Cucumis sativus), and muskmelon (C. melo). 

1 Prof. J. Ritzema Bos (1900) reports that Tylenchus dipsaci becomes so adapted to a host plant after 
growing on that species only for several generations that it will not attack with any severity the species 
upon which it grew before until several generations have passed. 

2 Stone and Smith, 1898, p. 30. 

217 



DISTRIBUTION OF ROOT-KNOT. 23 

The various families of plants represented in the foregoing list and 
the fact that the infections were obtained easily and very pronouncedly 
would seem to indicate that the nematode causing root-knot of the 
plants experimented with, including some of those most generally 
affected in the field, is not as yet very markedly differentiated into 
strains peculiar to certain hosts. It is still possible, and indeed quite 
likely, that had seeds of the same host as that furnishing the roots 
from which the nematodes came been sown in the pot along with the 
other seeds the latter would have shown less infection than the other 
plants. Unfortunately, however, various circumstances prevented 
this line of experiments from being carried out. 

Observations in the field seem to bear out the results of the pot 
experiments. The writer has been unable to detect any special adap- 
tation to any one species of plant. Indeed, peaches were attacked 
very badly when planted where cowpeas had been grown for several 
years. Figs and the Old World grape are the plants through which 
the parasite has been introduced into many new districts, which could 
hardly have been done so thoroughly and rapidly if the nematode 
had become in a manner specialized upon them. 

DISTRIBUTION OF ROOT-KNOT. 

Root-knot was first observed by Berkeley 1 on greenhouse plants 
in England [t was next reported by Greef 2 on out-of-doors plants 
in Germany. Since then it has been observed in many parts of 
Germany, France, Italy, Austria, Holland, Sweden, and Russia. 
In Africa it is abundant in parts of Algeria, occurring even in some 
of the Saharan oases, Egypt, German East Africa, Transvaal, Cape 
Colony, and Madagascar; in Asia it occurs widespread in India, 
Ceylon, and to some extent in China and Japan. In the East Indies, 
Java and Sumatra are badly infested. No authentic reports have 
been received of the presence of this pest in the Philippines, but it is 
probably to be found there. Several of the Australian States are 
infested, and the pest is not unknown in New Zealand. In South 
America it has been reported from Chile, Argentina, and Brazil. It 
seems also to be widespread throughout the West Indies. In Mexico 
it is prevalent at many points. 

In the United States the root-knot is to be found in sandy soil now 
or previously in cultivation in most parts of North Carolina, South 
Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, and 
Texas, as well as at many points in California. It is not abundant 
in New Mexico or Arizona, although proving destructive in some of 
the irrigated districts of the latter. It is very evidently of recent 
introduction there, as in many parts of Texas. In the interior of the 

i Berkeley, 1855. 2 Greef, 1864. 

217 



24 ROOT-KNOT AND ITS CONTROL. 

West the writer has observed it, only sporadically it is true, in Utah 
and Colorado and at one place in Nebraska. It is reported, and the 
writer has seen specimens, from Arkansas. Oklahoma, Tennessee, 
and Kentucky have no reports of it in the open, but it is probably 
present to some extent, since it is found along the Ohio River in 
West Virginia and also in northern Pennsylvania. It occurs, but not 
in great abundance, in Delaware, Maryland, and Virginia The New 
England States appear to be almost free from the trouble, so far as 
outdoor plants are concerned, although it has been observed in Con- 
necticut and Rhode Island. The most northerly points where it has 
been observed out of doors in this country are at various points in 
New York State, on ginseng and alfalfa; northern Indiana; Menomi- 
nee, in the Upper Peninsula of Michigan ; and the locality in Nebraska 
already mentioned. In the last three instances all the evidence indi- 
cates that the disease was directly imported from other localities and 
was not indigenous to that locality. The important point is, how- 
ever, and this will be reverted to, that this nematode is able to main- 
tain itself in regions where the winter's cold may be very intense 

All of the localities named above are those in which the root-knot 
nematode has been found out of doors, not merely on plants par- 
tially protected during the winter, but in soil not at all protected 
from the severest winter cold. In addition to these localities it is 
almost universally present in this country in greenhouses and has 
in a number of instances become more or less established out of 
doors in their immediate vicinity, where it is protected by compost 
heaps, etc., from the extreme cold. In the most northern States it 
need not be feared that the pest will ever become widely distributed. 

A careful study of the distribution of the disease convinces the 
writer that root-knot is of comparatively recent introduction in the 
regions west of the Mississippi. Indeed, it is possible to trace its 
arrival in parts of Texas, Arizona, and southern California, it having 
appeared in recent years after the land had been in cultivation for 
a long time with no signs of injury from such a pest. In Texas the 
introduction and spread of the nematode has been accomplished 
almost entirely by means of infected nursery stock, mainly figs, 
mulberries, and peaches; in Arizona and California figs and the 
Old World grape seem to be the responsible plants. The scattered 
localities in the North where the trouble occurs often reveal, on care- 
ful inquiry, the source of the infestation. Ginseng has been respon- 
sible for several outbreaks, the nematodes doubtless having been 
introduced in the moist earth in which the seeds were packed. In 
other cases nursery stock, such as peaches or even apples, has been 
responsible; sometimes the soil thrown out from greenhouses has 

217 



THE CAUSAL PARASITE. 25 

spread the trouble, and in some cases the manner of introduction 
can not be determined. 

Close analysis of all the earlier reports and of the existing distribu- 
tion of root-knot has convinced the writer that we have to deal with 
a pest originally tropical or subtropical in its distribution and not 
native to any part of the United States. In this the writer comes 
to a conclusion at variance with that of Neal, 1 who believed that it 
was native to the Southern States. If that were the case, however, 
it ought to be found on uncleared land where no crops have ever 
been grown, but that is not generally the case. Indeed, it is the 
general practice, when nematode-free land is needed, to go to un- 
cleared land. To be sure, nematodes are occasionally found in such 
land, but almost always it can be shown to have been previously in 
cultivation, perhaps many years ago, or to be so situated that soil 
from infested fields could be washed upon it. 

The general trade in exotic plants which began over a hundred 
years ago and grew rapidly, in the course of which ornamental and 
useful plants from the Tropics, especially of the Americas, were car- 
ried to European conservatories and gardens and also to our shores, 
may very probably have served to introduce the pest into the tem- 
perate regions of both the Old World and the New World. In all like- 
lihood the Spaniards introduced this nematode into Florida directly 
from the West Indies or Central America, for it is found in parts of 
southern Florida that were in cultivation more than 75 years ago, 
but where now dense forests have grown up, as well as in clearings 
with no signs of recent cultivation. Yet even here it does not seem 
to occur in land absolutely unused in the past. 

Whether the Old World or New World Tropics were the original 
home can not be decided now, as it is widely distributed in both. 
Perhaps its wide distribution in Africa, India, the East Indies, 
China, and Japan and the fact that another species of the same genus 
(Heterodera schacJitii Schmidt) is apparently native in Europe would 
warrant the conclusion that it is probably of Old World origin. 

THE CAUSAL PARASITE. 

Upon breaking across a medium-sized or large knot and holding 
the broken surface so as to reflect the light a close observer will often 
see one to many clear to almost pearly white rounded bodies, con- 
siderably smaller than half the diameter of a pinhead, projecting 
from the surface. With a hand lens they are easily seen, but for the 
unaided eye they are sometimes very difficult to detect, on account 
both of their minuteness and of their transparency. In knots 
that have been cut across they are usually not visible, as they col- 

l Neal, 1889. 
217 



26 ROOT-KNOT AND ITS CONTROL. 

lapse when touched by the knife. These objects are the mature 
females of the nematode Heterodera radicicola (Greef) Miiller. Each 
is capable of laying several hundred eggs, more than 500 having been 
counted by the writer in one case where the nematode was still 
actively laying eggs. 

EGG. 

The eggs (PL I, figs. 1 and 2) are ellipsoidal bodies, sometimes 
symmetrical, more often slightly curved, and therefore somewhat 
kidney shaped. They are usually a little over twice as long as broad. 
Out of 71 different lots of egg masses measured by the writer, repre- 
senting nematodes from 63 different hosts, the length varied from 
67 to 128 ^ and the width from 30 to 52.5 jx. The greatest ranges 
observed in any one lot of eggs were 67 to 108 by 33 to 42 /x, 88 to 
128 by 33 to 44 fi, 81 to 112 by 33.5 to 40 /x, and 84 to 119 by 35 to 
52.5 /x. These represented in each case eggs from the same nema- 
tode, showing how variable in size they may be. The average range 
of all measurements was 85 to 98 by 34 to 40 \x with an absolute 
average of more than 500 eggs measured of 92 by 38.4 /x. These 
dimensions agree closely with those given by Miiller, 1 who studied 
this nematode in Germany, his figures being 94 by 38 p.. On the 
other hand, Frank, 2 also working in Germany, gives the figures as 
80 by 40 /x. Stone and Smith 3 give the length as 100 /x. 

When the writer first examined the eggs from different hosts he 
thought that there might be a possibility of distinguishing different 
races of the nematode by the variations in the size of the eggs, but 
the variability in size, even among the eggs from the same nematode, 
soon demonstrated that no results of value could be obtained in 
this direction. It seemed to be true, however, that the smaller, 
less strongly developed females often produce the smaller eggs. 
Thus, a nematode situated near the surface of a root, where the 
pressure was not so great, was often larger and had larger eggs, but 
this rule has so many exceptions that it can not be considered as 
being in any way general. 

The egg consists of a densely granular body in which a lighter 
spot, the nucleus, can occasionally be seen, inclosed in a tough, elastic, 
transparent coat, or shell, probably chitinous in nature. When the 
mother nematode is so situated that she has plenty of room to de- 
posit her eggs so that they are not laid with difficulty, they usually 
leave her body unsegmented. On the other hand, if the eggs as 
they are laid are crowded together so that considerable force has to 
be used to lay each egg, the oviposition is delayed and segmenta- 
tion begins before the later eggs leave the body. Only exceptionally, 
however, do the eggs develop so far as to contain fully developed 

i Miiller, 1883. ' Frank, 1885. 3 Stone and Smith, 1898. 

217 



THE CAUSAL PARASITE. 27 

larvse by the time they are laid. Where this does occur it is mostly 
only the last eggs produced and which the mother nematode has not 
had the strength to force out against the large mass of eggs already 
laid. In this the root-knot nematode differs quite markedly from 
the sugar-beet nematode (Heterodera schachtii Schmidt), in which a 
comparatively large part of the eggs produced remain within the 
body of the mother and undergo segmentation and finally escape 
from the shell, eventually escaping to the outside through the open- 
ings in the body wall after the death of the old nematode. 

Segmentation of the eggs begins very soon in any case and proceeds 
rapidly. It was not determined exactly how long the embryonic 
development required, but it is apparently not over two or three 
days in warm weather (much longer in cool). 

The eggs were laid at the rate of 10 to 15 a day in the cases 
observed by the writer, although in some cases egg laying may pro- 
ceed even more rapidly. They are surrounded by a slimy or gelati- 
nous substance, which incloses them and evidently acts as a pro- 
tection. This is secreted by the nematode with the eggs, as was 
observed on isolated mature females under the microscope. It 
is at first quite liquid and colorless, but soon becomes rather firm 
and light brown in color toward the outside. This is the structure 
that has been called by some investigators the egg sack (Eiersack); 
for example, Voigt l and Strubell. 2 The latter applied the term to 
the similar structure in the sugar-beet nematode (Heterodera 
schachtii), and, erroneously, denied its occurrence in H. radicicola. 
Occasionally the remains of the male may be found entangled in this 
slimy mass. It is probable in such cases that after fertilizing the 
female the male died and when the eggs were laid the egg mass sur- 
rounded his remains. The eggs at the outer portion of the mass are 
usually either hatched or contain larvae, while those next to the body 
of the nematode are not segmented. 

This egg mass is sometimes as large as the adult female and can be 
seen readily when the latter partly projects from the root. 

LARVA. 

The larva (PL I, figs. 3 and 4) emerges from the egg through a hole 
which it pierces in the shell, usually at one end. It is a slender, 
cylindrical animal, blunt at the anterior and tapering at the poste- 
rior end to a pointed tail. The larvae when they emerge from the 
egg are 375 to 500 p. in length 3 and about 12 to 15 ja in greatest 

i Voigt, 1890. 

2 Strubell, 1888. 

s Stone and Smith (1898) give the length of the larva as 350 n, but this is considerably less than the meas- 
urements made by the writer. They give the egg length as 100 n, showing that they were not dealing 
with eggs below the normal size. 
217 



28 



ROOT-KNOT AND ITS CONTROL. 



thickness. The average length is 420 to 475 p.. The structure of the 
larva is comparatively simple, consisting essentially of a tube (the 
alimentary canal) within a tube (the bod} r wall), the space between 
(the body cavity) being filled with a liquid and minor structures 
(fig. 1). The body cavity has no opening to the exterior. The ali- 
mentary canal opens anteriorly at the end of the body, but posteri- 
orly it opens in the median ventral line about one-eighth of the dis- 
tance forward from the tip of the tail 
(i. e., 50 to 65 ;x). The body wall con- 
sists of an external cuticle and a dermal 
layer of cells beneath which are the 
four "fields" of obliquely longitudinal 
muscle cells. Longitudinal tissue 
masses springing inward from the der- 
mal layer at the median dorsal, ventral, 
and lateral lines separate the muscles 
into the four "muscle fields" men- 
tioned. Only occasionally the opening 
of the excretory canal can be made out 
in the larva, but it is quite distinct in 
the mature male. It is in the ventral 
median line, opposite or slightly pos- 
terior to the esophageal bulb. These 
details of structure are clearly shown in 
the accompanying text figures (figs. 1, 
2, and 3), contributed by Dr. N. A. 
Cobb. 

The alimentary canal consists first of 
a buccal spear (PI. I, fig. 4) 10 to 15 u. 
long (usually about 12 /*), a chitinous 
organ, pointed at the anterior end and 
with three small knobs at the posterior 
extremity and pierced its whole length 
by a fine canal. Connected with the 
basal knobs are retractile and exsertile 
muscles. This spear is used by the nem- 
atode in boring its way out of the egg 
and through plant tissues, and through it the nourishment is apparently 
drawn, for its canal is continuous with the lumen of the remainder of 
the alimentary canal. This spear lies in a cavity, the buccal cavity, 
from which it may be exserted. At the base of the spear begins the 
slender esophagus, 40 to 50 // long, which expands then into the thick, 
muscular- walled esophageal bulb (figs. 2 and 3). This is a stout, 
muscular body, often nearly spherical, but more often a little longer 

217 




X250 



Fig. l.—Heterodera radicicola. Half-grown 
female ( ?) individual shortly before the 
final molt: a, Anterior end; 6, spear; c, 
esophagus; d, esophageal bulb; e, nerve 
ring; /, excretory pore; g, gland; h, thick 
wall of alimentary canal; i, body wall; 
j, beginning of reproductive organs; k, 
anus. Magnified 250 diameters. Drawn 
by W. E. Chambers. 



THE CAUSAL PARASITE. 



29 



than broad, about 10 by 7 jul. The thick walls inclose a small lumen 
which can be expanded and contracted by the muscular action, thus 
acting in the manner of a pump in connection with the esophagus 
and spear (fig. 3). The expansion and contraction of the bulb are 
often synchronous with motions of 
the spear. Immediately behind the 
bulb the alimentary canal is rather 
narrow for a very short distance and 
then widens out rather abruptly into 
the comparatively thick-walled di- 
gestive portion which fills the body 






Fig. 2. — Anterior portion of the same nematode 
shown in figure 1: o, Anterior end; 6 and c, free 
and inclosed portions, respectively, of spear; d, 
esophagus; e, outer wall, and, /, central portion 
of esophageal bulb; g, nerve ring; h, second 
bulb; i, thickened wall of alimentary canal; 
j, excretory pore; fc, gland. Magnified 700 
diameters. Drawn by W. E. Chambers. 



Fig. 3. — Larva of Heterodera radicicoh: a, An- 
terior end; 6, c, and e, spear; d, buccal cavity; 
/, esophagus; g and h, outer and inner por- 
tions, respectively, of esophageal bulb; i, 
nerve ring; j, excretory pore; fc and I, lumen 
and thick wall, respectively, of alimentary 
canal; m, fat globule (?); n, anus; o, pos- 
terior extremity. Magnified 700 diameters. 
Drawn by W. E. Chambers. 



cavity and continues unchanged to a 
point shortly anterior to the anus. 
The anterior part of this digestive por- 
tion is not clearly marked off as a 
second bulb, as is the case in some 
species of Tylenchus. Immediately 
behind the esophageal bulb, surrounding the short, narrow portion of 
the canal, can be seen occasionally the nerve ring. About 25 to 40 /x 
anterior to the anus the walls begin to become thicker and the canal 
tapers, the anal opening itself being rather small. 



217 



30 ROOT-KNOT AND ITS CONTROL. 

Except anterior to the digestive portion of the alimentary canal 
the body cavity is small. There are no signs as yet of the repro- 
ductive organs, nor can the sexes be distinguished. 

The larvae are actively motile, but not so active as many of the free- 
living forms. Unlike the larva? of some nematodes parasitic upon 
plants, for example, Tylenchus tritici, 1 T. dipsaci, 2 and a species of 
Aphelenchus discovered by Dorsett 3 on the violet and studied by the 
writer, the larvae of Heterodera radicicola are not very resistant to 
unfavorable conditions. The other nematodes mentioned are unin- 
jured by desiccation for long periods, by cold, many acids, etc. Thus, 
the wheat nematode has been revived after having been left dry for 27 
years. The Aphelenchus referred to remained alive in kerosene 
emulsion for two days in contact with a drop of kerosene. Osmic- 
acid fixatives killed it but slowly, as was true of chromic acid, mer- 
curic chlorid, and other strong poisons. On the other hand, the 
larvae of Heterodera radicicola, although able to remain alive in water 
for a few days, soon die and decay, although damp or wet soil, pro- 
vided the air supply is good, is favorable to their existence. Drying 
out is usually fatal to them in a comparatively short time. 

The larvae of the root-knot nematode are able to remain alive in the 
soil for months without entering upon a parasitic existence. The 
writer has been unable, however, to find any evidence that they take 
any nourishment from the soil; at least they undergo no development 
until they enter the roots of some plant, for if the soil be kept free from 
vegetation for two years they all die. Even one year without food is 
sufficient to kill large numbers of them. 

In the normal course of development the larvae, having encoun- 
tered a root, seek its growing point and batter their way into it by the 
aid of the buccal spear (PL I, fig. 17). They then take up a position 
entirely within the root and parallel to its longitudinal axis, the 
anterior end pointing away from the root tip. This position may be 
in the plerome, or perhaps as frequently, if not more often, in the 
periblem. In the former case the nematode lies within the central 
cylinder as the root develops, in the latter case in the cortex. In 
either case the anterior end of the nematode is usually in close con- 
nection with the cells surrounding the conductive tissues. In the 
case of larvae which hatch from eggs produced within the root, some 
bore their way out into the surrounding soil and enter new roots, as 
described above, while others burrow along in the tissues of the root 
and settle down, usually in the fleshy cortex. Thus an old nematode 
gall will contain nematodes in all stages of development and at a 

i Davaine, 1857. Miinter, 1866. Needham, 1745, 1775. Baker, 1753. 
2 Ritzema Bos, 1892. 
» Dorsett, 1899. 
217 



THE CAUSAL PARASITE. 31 

depth below the surface of the root of even 5 or more centimeters. 
The latter has been observed by the writer in roots of sweet potato 
(Ipomoea batatas) at Miami, Fla. 

Within the tissues the larva becomes fixed in position and remains 
quiet except for occasional movements of the spear and esophageal 
bulb. Whether all the nourishment is taken through the hollow 
spear or some is absorbed directly through the skin was not deter- 
mined. It seems probable, however, that the former is the case, 
especially in view of the fact that the female occasionally bursts the 
surrounding tissues of the root, so that she lies outside the latter 
except for the anterior portion, which remains buried in the tissues. 

Growth begins almost immediately. This is mainly, however, in 
thickness and only slightly in length (PL I, figs. 5, 6, 7, and 8). By 
the time a gain of 10 per cent in length has taken place the thickness 
has increased five to ten fold. This increase in thickness is confined 
to the region anterior to the anal opening and in the main posterior 
to the esophageal bulb. The alimentary canal posterior to the bulb 
becomes greatly enlarged. In a week or ten days the larvae of both 
sexes are spindle shaped. By the end of the fifteenth to twentieth 
day the diameter is about a fourth of the length and the differentiation 
of the sexes becomes apparent (PL I, figs. 9 and 13). According to 
Stone and Smith * the female nematode sheds her skin four or five 
times during the course of development, the first time just before 
leaving the egg and the other two or three times before the final molt, 
when she becomes sexually mature. The writer has been unable to 
confirm this statement. In none of the specimens examined was any 
sign of shedding the skin apparent on leaving the egg, although on 
this point the evidence is slight, as special attention was not given to 
it. On the other hand, no trace of old skins could be found sur- 
rounding the developing larvae within the galls up to the time of dif- 
ferentiation of the sexes. It seems possible that the investigators 
referred to may have been misled by the fact that an injured nematode 
sometimes secretes a new cuticle underneath the old or on account of 
the circumstance that the molting may commence at one point long 
before it is visible elsewhere. If these extra molts do actually occur 
it seems strange that no signs are to be found of the cast-off skins 
around the nematode. 

The writer's observations lead him to the following conclusions: 
The sexes are alike (externally at least) up to about the fifteenth 
day, or sometimes longer. Then a new skin becomes visible under- 
neath the old, from which it becomes separated at various points. 
In the female the most marked change is that of the shape of the 
posterior end of the body, which no longer possesses the tail it had 

i Stone and Smith, 1898, p. 22. 
91294°— Bui. 217—11 3 



32 ROOT-KNOT AND ITS CONTROL. 

before the new skin was formed. At first the remnants of the old 
skin are visible as an empty skin attached to the rounded posterior 
portion of the nematode (PI. I, fig. 9), but soon the growth of the 
latter obliterates the cavity left and all signs of it disappear. The 
anus, which before this time occupied a median ventral position some 
distance anterior to the tip of the tail, now becomes terminal, and 
immediately ventral to it but also occupying a position almost ter- 
minal on the rounded posterior portion appears the prominent genital 
opening, a horizontal opening with two rather thick and prominent 
lips (PI. I, fig. 10). The anterior portion has undergone but little 
change. Apparently fertilization must take place at about this 
time, for soon the external genitalia become so modified that this 
would become impossible. The lips become smaller, the opening less 
prominent, and eggs begin to develop. 

Up to the last molt the larvae of both sexes are alike, at least ex- 
ternally. The writer's very numerous observations do not allow 
him to confirm the statement of Atkinson ' that the female can be 
distinguished before this period by the lack of a pointed tail, that of 
the male being pointed. In all the writer's observations, as pre- 
viously described, the larvae are indistinguishable until the last 
molt. Then the still small but sexually mature female may be seen, 
without a tail, in the old larval skin which has a tail. 

ADULT FEMALE. 

The mature female rapidly increases in thickness, becoming 
eventually flask shaped to pear shaped with a length of 400 to 1,300 [i 
and a thickness at the point of greatest diameter of 270 to 500 [x, 
or even 750// (PI. I, fig. 12). The average of many measurements 
is about 800 /* for the total length, 500 ji at the point of greatest diam- 
eter, the length of the less enlarged anterior portion being 240 \i 
and its diameter just before the region of great thickening begins 
150 \i. This not greatly enlarged anterior portion usually extends to 
a little posterior to the bulb. The body then enlarges abruptly, 
this posterior portion being approximately spherical. 

Up to the last molt the spear of the female retains the dimensions 
and shape it had in the larva. As is characteristic of all spear- 
bearing nematodes, the old spear is shed with the cuticle at the time of 
molting, a new spear being formed in its place. This new spear is 
usually smaller both in length and thickness than the larval spear, 
and the knobs at its base are less prominent. It is usually 10 to 12 // 
long as against 12 to 15 [i (rarely 10 //), characteristic of the larva. 

i Atkinson, 1889. 
217 



THE CAUSAL PARASITE. 33 

The fully mature egg-laying female is of a glistening pearly 
white color. The enlarged posterior portion is smooth and shows 
no markings, except that the internal organs are visible where they 
approach the surface. The comparatively little enlarged anterior 
portion shows faintly the transverse cuticular markings so charac- 
teristic of the mature male. 

The bulk of the body of the sexually mature but not yet egg- 
laying female is occupied by the enormously dilated alimentary canal 
(PI. I, fig. 11). The anus is a small round terminal opening, while 
the genital opening is a transverse slit slightly ventral to the anus 
and bordered by two more or less well-marked lips. This opens into 
a short, thick-walled vagina about 16 to 20 /i in diameter (including the 
walls). At its upper end it is abruptly contracted into a tube 8 to 
10 p. in diameter, which soon divides into two tubes, the uteri. These 
are at first slender but slightly coiled tubes, leading forward (usually 
lateroventrally) and gradually increasing in diameter. Just before the 
ovary is reached each uterus expands into a spherical portion, about 
16/z in diameter, apparently the receptaculum seminis. Above this 
lie the cylindrical ovaries filled with the rudimentary eggs in the 
form of a sort of parenchyma. At this time the whole reproductive 
system if straightened out would not be more than 300 to 400 /x 
long. After fertilization the uteri undergo a most remarkable elonga- 
tion and become very much coiled and tangled as they become 
filled with the fertilized ova. Although the body of the nematode 
increases rapidly in thickness, the increased space thus afforded is 
not sufficient, the alimentary canal becomes pushed to one side, and 
much of the space originally occupied by it is occupied by the uteri. 

Egg laying had already begun, in the earliest cases observed by 
the writer, 29 days after the seed of the host plant (Pisum sativum, 
the garden pea) in these experiments was planted in soil known to 
be infested with the nematodes. Since germination of the seed is 
not immediate it is probably safe to assert that during warm weather 
the period from the time the larva enters the root until it begins 
egg laying is not over 25 days. This is somewhat longer during 
cooler weather, i. e., in the early spring and in autumn. 

In most cases the greater part of the eggs are laid in an unseg- 
mented condition. However, if the nematode is buried deeply in 
the tissues so that their pressure impedes egg laying, the eggs may 
develop and the larvae escape still within the body of the mother, so 
that the latter may be viviparous. The last few eggs often develop 
in a similar manner, the nematode having evidently become so weak 
that she could not deposit them before they underwent development. 

217 



34 ROOT-KNOT AND ITS CONTROL. 

MALE. 

The development of the male after the larval stage differs greatly 
from that of the female. Within the old larval cuticle a new cuticle 
is formed. The nematode pulls itself away from the old skin, remain- 
ing inclosed by it, however. The tail is rounded here, too, but the 
anus is ventral instead of terminal. The whole body now elongates 
very rapidly, becoming correspondingly slender (PI. I, figs. 13 and 14). 
This necessitates a coiling in order still to remain within the old skin, 
until it is coiled two or three times. When this development is com- 
plete (PL I, fig. 15) it breaks its way out of the old cuticle, which has 
retained its larval shape, and passes through the tissues and probably 
even outside of the root in search of a female. Just prior to leaving 
the old larval skin after undergoing this metamorphosis the nematode 
does not molt again, as some assert. 

The mature male differs greatly in many particulars from its appear- 
ance just previous to the last molt. The form is about like that of 
the larva on emerging from the egg, i. e., long and slender, differing, 
however, in the greater size and in the short, rounded tail. The 
length is usually 1,200 to 1,500 p, the thickness 30 to 36 p. The tail 
is short and rounded, not tapering, the distance from the anal open- 
ing to the posterior end of the body being not more than 13 to 18 p. 
The cuticle over the whole body is very distinctly marked with trans- 
verse rings extending entirely around the body and 2 to 2.5 p apart 
(shown in section in PI. I, fig. 16). Except in profile it is only the 
furrows between the projecting segments of cuticle that are visible. 
These cuticular rings, which are also visible on the anterior portion 
of the mature female, are not visible, at least at ordinary magnifica- 
tion, in the larva?. 

The alimentary canal is essentially as in the young larva. The 
spear, however, deserves special notice. It is larger than in the larval 
stage or than in the mature female, being usually about 24 p in 
length (rarely as short as 18 p. or as long as 28 p). The knobs at its 
base are prominent. Above the knobs the sides are parallel for about 
half way and then taper to the finely pointed tip. The canal through 
the spear is rather distinct. The body wall is about 1.5 p thick. 
However, at the truncate anterior end it is between 5 and 6 p thick. 
The anterior 2.5 p of this is a sort of hood, or cap, set off from the 
rest of the body by a sharp furrow. Lying in the terminal body 
wall, well below this hood and projecting but slightly into it, is a 
series of six radiating perforated lamellae (apparently chitinous in 
nature), narrow at their anterior ends and broad basally. Viewed 
from the side they are approximately right triangles, the hypotenuse 
being somewhat wavy. The bases of the lamellae radiate from a 

217 



THE CAUSAL PARASITE. 35 

common center, and the upright legs of the triangle surround a canal 
through which the spear passes. The bases are united into a small 
ring just around this canal and another ring unites the outer ends of 
the basal legs (PI. I, fig. 16). Looked at from the anterior or pos- 
terior direction this apparatus resembles a wheel with six spokes. 
Distinct muscle strands run from the rim of this wheel to the knobs 
of the spear, as well as to the point where it begins to taper. It is 
probable that this peculiar organ is to help support and guide the 
spear as the male is battering his way through the tissues. A similar 
apparatus is present in Heterodera schacMii, the sugar-beet nematode. 
It was imperfectly described by Strubell, 1 but the writer's observa- 
tion shows it to be essentially the same as in the root-knot nematode. 
It has also been reported, but not correctly described, for a Tylenchus 
species. 

The reproductive organs of the male consist in all cases examined 
by the writer of a single testis, a tube blind at the anterior end and 
running parallel to the alimentary canal, into which it opens just 
before the anal opening is reached. Atkinson reports that there are 
two of these reproductive organs, as is the case with some other 
nematodes. In all the specimens examined by the writer, however, 
including specimens from Indiana, South Carolina, and Florida, using 
the oil immersion lens and viewing the nematodes from different 
sides, there was not the slightest evidence of a second testis. Cobb 2 
also mentions its presence, and as both he and Atkinson are accurate 
observers it must be that sometimes this occurs. In fact, Atkinson 
himself later found specimens in which the testis was single. 3 Accord- 
ing to the writer's own observation the right testis is the one that is 
missing, as the one present is placed somewhat asymmetrically, lying 
nearly in the left half of the body. 

Lying on either side of the posterior portion of the alimentary canal 
and with their points entering the cloacal chamber are two peculiar, 
somewhat sickle-shaped bodies, the spicules. These are curved bodies, 
tapering toward the posterior end, about 35 /« long, measured on the 
chord connecting the two ends. No accessory piece is present, 
although a thickening near the apical portion may represent one fused 
with the spicules. These spicules are of use only during the sexual 
process. 

The excretory canal is plainly visible in the left lateral line, open- 
ing ventrally in the median line 160 to 170 pt from the anterior end 
of the body. 

It seems probable that the mature males take little or no food 
and that they perish after having performed their function. The 
reason for this supposition is the fact that one often finds still actively 

i Strubell, 1888. 2 Cobb, 1902. 3 Atkinson, 1889; see also Atkinson, 1896. 

217 



36 ROOT-KNOT AND ITS CONTROL. 

moving males in wliich the alimentary canal posterior to the bulb, 
or even including it, has entirely disintegrated, leaving the body cavity 
filled with a granular disorganized mass except for the long testis, 
wliich extends nearly to the esophageal bulb. The large buccal spear 
with its complicated guiding apparatus is doubtless to enable the 
animal to batter its way through the root tissues in its search for the 
female, as a much smaller spear serves the female for obtaining the 
necessary food. 

OVERWINTERING. 

The stage in wliich this nematode overwinters was made the object 
of considerable study. In the galls on annual plants examined in 
November it was found that in almost all cases the mature or partly 
developed nematodes, as well as the eggs, were dead, in many cases 
being filled with fungous threads. Larvae, however, alive and 
actively motile, were found in abundance in and around the galls. 
It is probable, therefore, that it is in the larval stage that the nema- 
todes from annual plants pass the winter, probably descending into 
the lower levels of the soil to avoid the cold. This latter point, 
however, was not determined. In cases where the death of the top 
of the plant had caused the death of the roots, the nematodes in the 
roots soon died also. 

In roots of perennial plants, for example, European grape, fig, etc., 
the writer has repeatedly found living female nematodes in nearly 
or quite complete development at various periods in the winter and 
early spring, showing that in such roots the nematodes may survive 
not only in the larval stage, as previously described, but also as 
mature females ready to begin egg laying as soon as the weather 
becomes favorable. 

COMPARISON WITH HETERODERA SCHACHTII. 

In view of the fact that some authors 1 have questioned the correct- 
ness of keeping separate the two species Heterodera schaclitii, the 
sugar-beet nematode, and H. radicicola, the cause of root-knot, it 
will be well to give briefly an account of the points of difference, 
especially since the writer has found the former to be a serious pest 
at several points in California and Utah, while the latter has been 
found as a serious sugar-beet pest at some other points. In tabular 
form the main differences are easy to point out. 

i Stone and Smith, 1898; Atkinson, 1896. 
217 



THE CAUSAL PARASITE. 
Table II. — Differences between Eeterodera schachtii and H. radicicola. 



37 



Points. 


Heterodera schachtii. 


Heterodera radicicola. 




No galls. 

External, anterior end only within 
tissues of root. 

Mostly lemon shaped, dull and flaky 
in appearance, no trace of transverse 
rings. 

Part deposited outside body, but most 

developing within it. 
Buccal spear about 25 p (PI. I, figs. 18 

and 19). 
Buccal spear about 30 p (according to 

Strubell, 1888). 




Location of mature fe- 
male. 

Shape of female, external 
appearance, etc. 


Usually entirely within tissues of root, 
more rarely the posterior portion, 
very rarely nearly the whole body 
external. 

Pear or flask shaped, glistening and 
pearly white, transverse rings of 
cuticle often visible on anterior por- 
tion. 

All but the last few deposited outside 
the body. 

Buccal spear 10 to 15 p, mostly 12 to 15 p 
(PI. I, figs. 3 and 4). 

Buccal spear mostly about 24 p. 




Mature male 





That these nematodes are not the same is readily seen when they 
occur on the sugar beet. The one causes no conspicuous galls while 
the other makes the galls so characteristic of root-knot (PI. II, fig. 1). 
Both are very destructive pests of this host, and there is not much 
choice as to which is the more harmful. Another difference not 
mentioned above is that H. schachtii, perhaps by virtue of its more 
powerful spear, is able to thrive and spread in stiffer soils than does 
H. radicicola. In Plate I the figures for the larvae of Heterodera 
radicicola (figs. 3 and 4) and H. schachtii (figs. 18 and 19) are drawn 
to the same scale, respectively. The difference between the two 
species was emphasized in tabular form by Voigt in 1890. 

METHODS OF SPREAD. 

The larva of Heterodera radicicola is capable of active movement 
in the soil, and in this manner doubtless the disease is slowly spread. 
From some experiments made by Frank 1 he estimated the rate of 
progress at about 3 cm. per week. This would amount, during the 
warm weather, in which infection occurs, say May 1 to September 
15, to about 75 cm., or about 30 inches. These figures are probably 
far too low. However, it is not through their own efforts that these 
nematodes are mainly spread. There are many means of transporta- 
tion at their disposal. A very frequent one is running water. Thus, 
a field previously free from the pest sometimes shows its presence 
in those spots where surface water at a time of heavy rains has 
deposited a lot of soil from an infested field lying higher up. In this 
way the pest has been carried from infested fields even to uncultivated 
woods, as observed by the writer at one place. It has been suggested 
that heavy winds carrying large quantities of soil from one field to 
another may also transfer the nematodes, but in view of their sus- 
ceptibility to injury by drying, this seems little likely. Especially is 



i Frank, 1885. 



217 



38 ROOT-KNOT AND ITS CONTROL. 

this unlikely since the larvae shun dry soil, and so would not be 
present in that part of the soil which is dry enough to be transported 
by the wind. More effective as means of transportation are the 
hoofs of animals, wheels of vehicles, farm implements, and men's 
boots. It is difficult to see how it would be possible to avoid conveying 
living nematode larvae from one field to another on farm implements 
if they are left, as is too often the case, uncleaned on being trans- 
ferred from one field to the next. Thus, a wagon and horses going 
from one field to another would, if the soil were at all damp, carry 
some of the damp earth, probably containing nematode larvae, with 
them. 

The foregoing explains the spread of nematodes after they have 
once been introduced into a locality. The introduction of nematodes 
into a new locality, however, must have some other manner of accom- 
plishment. This seems to be in most cases along with nursery stock. 
Thus, the writer found that in parts of Texas the nematode appeared 
first in the soil near fig and mulberry trees obtained from farther 
east, which were noticed at the time of planting, several years ago, 
to have knotted roots. In this way the soil near the trees became 
infested and thence the disease spread, a9 previously described, to 
different points in the locality. Perhaps east of the irrigated districts 
the fig, mulberry, and peach are responsible more than any other 
plants for the spread of the disease. Since the putting into effect of 
good nursery inspection much of this source of infection has been cut 
off. In the irrigated districts of Arizona and California the vine was 
observed in several cases to be the plant at fault. The strawberry 
has been observed at a few points in the East as the plant upon which 
the pest was introduced. It is often badly affected without showing 
much injury. A case has been called to the writer's attention in 
which the disease was introduced into a garden in Washington, D. C, 
by asparagus roots from an infested field. The wide distribution of 
the disease in ginseng plantations is doubtless due to the setting out of 
small rooted plants from infested regions, as well as to the practice 
of some growers of packing the seed in damp earth. Should this 
come, as is natural, from the vicinity of the ginseng bed and this 
be affected by nematodes, the danger of sending nematodes along 
with the seeds is very great. The dirt used for packing is naturally 
thrown out at the point where the seeds are planted, and thus the 
larvae, if present, are able to enter the soil and infect the young gin- 
seng seedlings. Seed potatoes are also another known source of 
introduction of the disease. 1 In a personal communication Dr. N. A. 

i Lounsbury (1904) regards the potato as perhaps the chief source of introduction and spread of this dis- 
ease in South Africa. 
217 






THE CAUSAL PARASITE. 39 

Cobb expresses the same opinion based on his observations in New 
South Wales. 1 

For the North, where root-knot is mostly confined to greenhouses 
and hotbeds and their vicinity, perhaps one of the chief sources of 
infection is the soil that is thrown out of these beds at the end of the 
season. This soil, if infested, will spread the disease in the imme- 
diate vicinity, especially if it be put near some manure pile or compost 
heap which keeps the ground damp and warm during the winter. 

EFFECT ON THE HOST. 

The effect upon the root of the presence within it of the young 
nematode is usually the hypertrophy of some of the tissues. The 
parenchyma cells become abnormally large and multinucleate, 2 
sometimes only a few, at other times a great many cells being involved 
in this hypertrophy. This abnormal enlargement of the cells leads 
to a displacement of the various tissue elements, so that the tracheary 
cells and vessels become separated and also show lateral displace- 
ment and often much distortion. Often in bad cases individual cells 
of a tracheary nature will occur entirely separated from others of the 
same kind. The amount of hypertrophic enlargement of the root 
depends upon the host on the one hand and upon the number of 
nematodes entering the root in the same vicinity on the other. In 
some roots the swelling is barely noticeable and is so small that as 
the female nematode enlarges she eventually is inclosed in the root 
only by the narrow anterior third of the body, the remainder being 
entirely external, in this particular showing great similarity to the 
sugar-beet nematode, whose galls are always of this nature. More 
often, however, the hypertrophy is so pronounced that the mature 
female is entirely concealed or reaches the surface only at the extreme 
posterior portion of the body. If many nematodes are present in 
the same general region of a susceptible root, the gall may be many 
times the normal size of the root (PL II, fig. 2). These galls are at 
first of soft tissues, but in some woody plants, the European elm, for 
example, some of the hypertrophied cells become lignified, inclosing 
the female nematode in a woody prison from which in all probability 
the larvae would be unable to escape should egg laying continue 
after the lignification has begun. The structure of such a gall is like 
that of the burls that often occur on various trees. 

A very frequent phenomenon, but one that is by no means uni- 
versal or characteristic of any one group of plants, is the formation 
of numerous lateral rootlets above the gall. This is doubtless due 

i The writer's attention has been called to the fact that in certain of the irrigated districts of the West 
this nematode has become a very serious potato trouble. On one occasion several carloads of potatoes 
were rejected on account of being infested with it. 

2 Tischler, 1902. 
217 



40 ROOT-KNOT AND ITS CONTROL. 

to the disturbed and to a large extent interrupted water supply 
and to the accumulation above the gall of food substances which 
would normally pass on to the root tip. They accordingly are made 
use of in the formation of lateral roots at that point. It is probably 
not different in its nature from the adventitious root formation in cot- 
ton and other plants just above the point of entry of the wilt fungus 
( Neocosmospora vasinfecta) l or, in fact, from that occurring when 
the end of a root is cut off or mechanically injured. The shape 
or size of the gall does not seem to depend upon the place the plant 
occupies in the current schemes of classification. The statement 
of Frank 2 that the galls of the dicotyledons are mostly of the round, 
tuberlike type, with lateral rootlets, while those of the monocoty- 
ledons are mostly spindle shaped, without lateral rootlets, is not 
confirmed by the writer's observations. Galls of both types may 
be found on the same plant (PI. Ill, figs. 1 and 2) and appear to 
owe their differences to the number of nematodes entering at a given 
point, to the age and rapidity of growth of the root, and perhaps to 
other causes. On both the beet and the radish, as well as on many 
other plants, both types of galls and all gradations between may be 
found. Entrance to the plant by the larvae is not confined to root 
tips or to passage from galls to the adjacent healthy tissues, although 
these are the usual ways by which a nematode reaches the point 
where it undergoes its subsequent development. Nematodes are 
also able to bore from the outside directly into the tender tissues 
of other parts of the roots, and even into stems. Thus, not only are 
the roots of potatoes attacked but even the tubers, while some- 
times the prostrate stems of tomato plants as well as those buried 
beneath the ground in setting out the young plants are badly 
knotted. Indeed, Senor Romulo Escobar, of the Mexican Ministry 
of Agriculture, informs the writer by letter that in the State of Nuevo 
Leon the roots, stems, leaves, and even fruits of the watermelon are 
attacked when they are in contact with the ground. This is excep- 
tional, however, and is possible only where the nematodes are very 
abundant and when the surface of the soil is constantly moist, so 
that they are in its uppermost layers. 

Through the kindness of Mr. W. K. Winterhalter, then consulting 
agriculturist of the American Beet-Sugar Co., at Rocky Ford, Colo., 
analyses were made of sugar beets badly affected with root-knot 
and of healthy beets from the same field. Strange to say, in six 
samples each of healthy and diseased beets the average sugar 
content differed less than one-fifth of 1 per cent of the total weight 
of the beet, while the percentage of purity was equally as close in 
the two lots. In these points there also seems to be a marked dis- 

> Orton, 1902, p. 10, fig. 1. > Frank, 1885. 

217 



CONDITIONS FAVORING ROOT-KNOT. 41 

tinction between the root-knot nematode and the true sugar-beet 
nematode (Heterodera schacJitii), for the latter's presence not only 
reduces the size of the affected beets, but also greatly reduces their 
sugar content and usually lowers also the purity. 

The greatest depth at which Frank observed nematode galls was 
33 centimeters (about 13 inches). On the other hand, the writer 
finds that they may occur more than a yard below the surface of the 
soil. To be sure, these are only scattering galls, for the great major- 
ity of the nematode galls occur in the first foot of the soil. Indeed, 
in practical culture it has been found that if trees can be forced to 
root extensively at a depth of 16 inches or more they suffer but 
little from root-knot o 

CONDITIONS FAVORING ROOT-KNOT. 

SOIL. 

Root-knot is essentially a disease of light soils. Wherever the 
soil is sandy or contains a fairly large proportion of sand, other con- 
ditions being favorable, the root-knot nematode may be expected 
to thrive when once introduced. In heavy soils, on the other hand, 
the disease seems never to be serious. In some of the writer's 
experiments affected plants were planted in pots of stiff clay soils, 
and not only was it almost impossible to obtain infection of sus- 
ceptible plants placed in close proximity in the same pots, but even 
on the diseased plants the new roots remained free from the trouble. 
Similar experiences have been reported to the writer from various 
parts of the country where diseased trees were set out in stiff soil 
and after a few years seemed to be entirely free from the trouble. 
Contradictory statements sometimes find their way into print, but 
they are explicable in most cases when one understands the great 
popular confusion in the use of the words "heavy," "stiff," and 
"light" as applied to soils. Thus, in parts of Florida and South 
Carolina a very sandy, yellow soil containing only enough clay to 
hold it together while moist, is called "clay" or "heavy soil." It 
is clayey, to be sure, compared with some of the soils thereabouts, 
for sometimes the latter are almost pure sand. "Light" and 
"heavy" in the sense used in this bulletin have reference to those 
soils containing, respectively, little and much clay. Soils that dry 
out rather quickly, that do not cake hard on drying, and that are 
easily crumbled to a fine granular mass are favorable to these nema- 
todes, while the reverse is the case for the difficultly permeable, 
hard-caking, clayey soils. This applies only to the root-knot nema- 
todes, as the writer's investigations have not gone into this point 
with reference to other sorts. It is known that the sugar-beet 
nematode will thrive in some of the heavier as well as in light soils. 

217 



42 ROOT-KNOT AND ITS CONTROL. 

MOISTURE. 

A certain degree of moisture is necessary for the maintenance of the 
life of the nematode in the soil. Experiments by the writer, Frank, 1 
and others have shown that the larvse of the root-knot nematode, 
unlike those of many other nematodes, are destroyed by being dried 
in the laboratory. Observations by the writer in New Mexico, Ari- 
zona, and California confirm this abundantly, for in those communi- 
ties the root-knot is practically confined to the irrigated land. This 
does not mean that the soil must be wet, for that is not necessary. 
The soil, however, must have sufficient moisture in it to be properly 
called a moist soil, though not enough to fill the air spaces and inter- 
fere with proper aeration. Thus, we have reports from South Africa, 2 
Argentina, 3 and Chile 4 which state that the nematodes grow only in 
wet soils. This, in the light of conditions existing in America, evi- 
dently means not what we would call wet, but merely moist, in the 
eastern and southern part of the United States, but what many people 
in irrigated districts would not hesitate to call wet in contradistinc- 
tion to the dry, unirrigated soils. Prof. P. H. Rolfs, 5 Dr. N. A. Cobb, 
and others report experiments which would seem to prove that dry- 
ing of nematode-containing soil does not entirely kill out the Hetero- 
dera radicicola. This will be discussed more in detail later. 

On the other hand, soils that are water-logged for a considerable 
part of each year are usually free from the trouble. Some observa- 
tions on the effects of floods on nematodes led the writer to believe 
that flooding for a few days would destroy them, but field experiments 
in Arizona and California showed that keeping the soil submerged for 
five days was not sufficient to kill out the nematodes, at least not 
those inclosed within the root galls of the trees and vines growing in 
the fields. Yet it is certain that very wet soils are free where this is 
long continued, and long periods of flooding kill out the nematodes. 
Thus, in the Everglades of southern Florida there occur islands, parts 
of which are never flooded and parts of which are out of the water 
ordinarily, but submerged for two to six months of the year. Truck 
growers occupy some of these islands and find that the root-knot 
nematode is abundant above the high-water level — i. e., where the 
land is never flooded, but absent in the zone that is flooded every year. 

TEMPERATURE. 

As long as the soil is not too dry, the higher the temperature the 
more actively the nematodes seem to develop. On the other hand, 
they seem to become practically inactive when the soil temperature 
falls below 50° F. Yet they are capable of remaining alive when 

> Frank, 1885. 2 Lounsbury, 1904. » Huergo, 1902, 1906. * Lavergne, 1901. & Rolfs, 1894. 
217 



CONDITIONS FAVORING BOOT-KNOT. 43 

exposed to great cold. The writer saw root-knot abundant on gin- 
seng in a slat shed in Menominee, Mich., where the soil a year or so 
before froze to a depth of more than 3 feet and where outside the 
shed water pipes 6 feet beneath the surface were frozen, so the writer 
was informed. In spite of this cold the nematode injuries were bad 
the next year. In York, Nebr., where the temperature goes below 
zero every year and sometimes reaches nearly or quite to —30° F., 
this nematode survived the winter in peony roots which remained 
out of doors without protection. In New York State ginseng and 
alfalfa are both more or less affected with root-knot, while in West 
Virginia, along the Ohio River, clover is badly affected. It thus 
becomes apparent that cold alone does not destroy the pest in the 
soil. To be sure, Bailey 1 placed soil containing root-knot nematodes 
in boxes and set some of the boxes out of doors through the winter. 
In the spring the boxes kept indoors still had living nematodes, as 
shown by gall formations upon plants grown from seeds sown there, 
while the boxes left out of doors were free from nematodes. It seems 
probable that the soil in this case dried out in the freezing process 
sufficiently to kill the nematodes. Ordinarily, however, the frozen 
soil remains in connection with soil moisture below, and so the drying 
out and consequent destruction of nematodes does not occur. 

The root-knot nematode does not become active in the soil and 
begin to penetrate the roots of susceptible plants until the soil begins 
to be warm. In the tropical and subtropical regions plants are sub- 
ject to attack the year around, but the farther north one passes the 
longer is the winter period of comparative immunity from injury by 
this pest. Thus, in Miami, Fla., there is no dormant period for the 
nematode. In northern Florida, however, crops planted in the latter 
part of November or in December show comparatively little injury, 
nor does the injury begin to be severe until the middle of February or 
early in March. On the other hand, plants sown in October are in- 
fected before the soil becomes cool and are badly injured, the nema- 
todes continuing to develop and spread within the tissues when it is too 
cool for them to spread outside through the soil. AtMonetta, S. C, 
about half way between Columbia and Augusta, Ga., in the writer's 
experiments no infection by nematodes could be obtained before the 
middle of April, while it was the middle of May before they became 
really active. By the end of September or the middle of October 
their activity had begun to decline. 

Frank 2 assumed that the chief period of infection was in the spring. 
He was in error in this statement, for the writer's experiments show 
that the nematodes are more active in midsummer and that infec- 

» Bailey, 1892, pp. 157-158. * Frank, 1885. 

217 



44 ROOT-KNOT AND ITS CONTROL. 

tions occur more freely the warmer the weather, except where lack of 
rain permits the soil to dry out, in which case both plants and 
nematodes cease to thrive. 

CONTROL OF ROOT-KNOT. 

The problem of the control of root-knot is one that varies much 
according to the place infested, the kind of plants grown, the methods 
of culture followed, etc. We may distinguish between small, inten- 
sively cultivated lots of soil, such as we find in greenhouses, hotbeds, 
and seed beds, and field culture. Each group may be subdivided in 
accordance with the answer to the question whether the crops are 
annual or long lived. For the first great division, owing to the value 
of the crops raised and the amount of capital invested, methods of 
combating a disease may be used that would be barred from field 
crops or other crops on larger areas of land, because the expense would 
not be justified in view of the comparatively low earning power of 
the land. Furthermore, the actual monetary loss to the crop due to 
a given disease may be far greater in the restricted areas of intensive 
culture than in large fields where each plant is of relatively less 
value. So, for example, root-knot may affect a field of cowpeas 
and actually reduce the crop one-half, but unless the field were very 
large that might not equal the loss sustained by a grower of cucumbers, 
lettuce, or tomatoes whose whole greenhouse crop has been totally 
destroyed by the same pest. 

GREENHOUSES, SEED BEDS, ETC. 
LIVE STEAM. 

Probably the most satisfactory method for destroying the root- 
knot in greenhouses and seed beds is the use of live steam under 
considerable pressure. This has been advocated by various persons, 
viz, May, Galloway, Selby, and Rudd, 1 but it was as a result of care- 
ful experiments by Stone and Smith : that it became generally used. 
The method recommended by them is a modification of that recom- 
mended by Galloway and others. The scheme is essentially as fol- 
lows : At the bottom of the bench or bed are laid either iron pipes 
perforated with -j^-inch holes every few inches or drain tiles. Live 
steam is passed into these and escaping from the holes of the iron pipes 
or between the ends of adjacent tiles heats the soil to such a degree 
that all animals and most plants (except, of course, bacterial spores) 
are killed. The pipes must be placed at intervals short enough to 
permit the spaces between the rows of piping to be thoroughly per- 
meated by the steam. This distance varies with the soil, but 12 

i May, 18%; Galloway, 1897; Rudd, 1893; Selby, 1896. 3 Stone and Smitn, 1898. 

217 



CONTROL OF ROOT-KNOT. 45 

inches is close enough for all general purposes, and even 2 feet is not 
too far in deep beds if the sterilization is kept up long enough. The 
bed should be covered with straw, boards, sacking, or something of 
the kind to permit the upper layer of soil to become heated through. 
The pipes or tiles in the soil should be arranged lengthwise in the 
beds, with the steam inlet in a crosspiece of piping running across the 
bed, from which the longitudinal rows take their origin. A similar 
crosspiece at the other end may be used, but is not absolutely neces- 
sary. There should be no open ends of pipes or tiles; otherwise all 
the steam will escape out of these and not through the cracks or small 
holes. Depending upon the pressure of steam used, the time neces- 
sary for sterilization will vary from half an hour to even two hours 
when the pressure is poor. 

A method often recommended to determine whether the steam has 
passed long enough, and one that has considerable merit, is to bury 
raw potatoes at the surface of the soil underneath the covering of 
straw, boards, or sacking. When all these potatoes are found to be 
cooked the steam can safely be turned off. Stone and Smith recom- 
mend the use of a special boiler so that steam at fairly high pressure 
can be used, not under 40 pounds per square inch, preferably more. 
Even 80 to 100 pounds pressure is not too high if obtainable, as it 
shortens the time necessary and also prevents the soil from becoming 
as wet as with lower pressure. 

Not only are all nematodes killed b} 7- this treatment, but also all 
insects and other noxious animals, as well as all fungi and their spores. 
Many bacteria are killed, too, but not all of their spores, the survival 
of the latter being desirable in view of what we know of the value 
of soil bacteria. 

This method has some disadvantages. Thus, it can not be used 
for beds occupied by living plants. Furthermore, care must be 
taken on the one hand not to leave the soil soggy and on the other 
not to dry it out too much. The latter is, however, a much less seri- 
ous matter than the former. 

FRESH SOIL. 

For greenhouses, cold frames, seed beds, etc., where a steam-heating 
plant is lacking and where it would not pay to incur the expense 
of installing a boiler for the purpose of using it for soil sterilization, 
the desired results can be obtained by the use of fresh soil each year. 
This should be taken from some place in the woods or from a field 
where the nematode is known not to occur. The old soil should be 
placed where it can do no harm in the way of spreading the disease. 
If it can be allowed to become perfectly dry for some weeks before 
taking it out, the danger from the old soil is greatly reduced. The 

217 



46 ROOT-KNOT AND ITS CONTROL. 

framework of the beds should be thoroughly whitewashed with strong, 
hot whitewash, freshly made from good quicklime, or it may be 
painted with formaldehyde or some other disinfectant of this nature. 
This is to kill all larvae or eggs that might be in the dirt adhering to 
the cracks. In selecting new soil it will always be well to examine 
the roots of susceptible plants growing where the soil is to be obtained 
in order to determine whether or not root-knot is present. This 
method has given good satisfaction where carried out in the North. 
It is applicable, however, only to small greenhouses that do not 
require much new soil. Large greenhouses can be far better taken 
care of by sterilizing the soil in the benches. 

It often happens that to obtain fresh soil is not desirable in view 
of the character of the soil in the vicinity. Perhaps it has taken 
some years to bring up the soil in the beds to the desired lightness, 
humus content, etc., and to have to take new soil every year would 
be a hardship. In such cases steaming should be made use of if pos- 
sible. If it is not feasible, a formaldehyde solution has shown itself 
of considerable value. 

FORMALDEHYDE. 

The formaldehyde method consists essentially of treating the soil 
with a weak solution of commercial formaldehyde (or formalin). It 
has been found that a solution of 1 part commercial (36 to 40 per cent) 
formaldehyde in 100 parts water is effective against the root-knot 
nematode in shallow beds when applied at the rate of 1 to 1^ gallons 
(or more in the case of very absorbent soils) to every square yard of 
soil surface. For deep beds the quantity must be increased. Care 
must be taken that all parts of the soil are reached and thoroughly 
wetted by the solution. Upon the thoroughness with which it is done 
depends largely the success of the process. After the formaldehyde 
solution has soaked in the soil should be thoroughly stirred, so that 
all parts may be exposed to the disinfectant. Before setting into the 
soil any plants or sowing any seeds the excess of formaldehyde must 
be allowed to escape by evaporation or, if necessary, be washed out by 
flooding the bed. The former is preferable. The writer has not found 
the germination of seeds interfered with when 10 days are allowed to 
elapse between the treatment and the sowing of the seeds, especially 
if the soil be allowed to become rather dry and be stirred in the mean- 
while. 

This formaldehyde treatment has been used with success at the 
Ohio Agricultural Experiment Station 1 in the forcing house and seed 
beds. It was applied primarily to prevent certain damping-off fungi 
from destroying the seedlings, but it was found that the nematodes 
were sometimes destroyed also or greatly reduced in numbers. How- 

> Selby, 1906. 
217 



CONTROL OF ROOT-KNOT. 47 

ever, as a means of combating nematodes it is not recommended by 
Prof. Selby. The strength of the solution used there was about 1 to 
1£ parts commercial formaldehyde to 400 of water, which is less than 
that found to be really effective against this nematode. 

The treatment of living plants in the greenhouse to destroy root- 
knot is fraught with considerable difficulty. Means that will destroy 
the nematodes are mostly injurious to the plants containing them. 
Thus, steaming or drying and freezing the soil can not be thought of, 
as these processes are fatal to the plants. So, too, the use of carbon 
bisulphid has in a similar way proved not feasible. It is still possible, 
however, that certain plants less susceptible to this chemical, if per- 
fectly dormant and rather dry, might escape without serious injury 
when enough of it was used to kill the nematodes present. This must 
be determined by experiment. Under certain conditions the use of 
the formaldehyde solution has been found efficacious with some kinds 
of roses. Many plants are killed outright by the treatment, but roses, 
at least some sorts, are less susceptible to injury. The first experi- 
ments in this line were performed in February, 1902, in the green- 
houses of Mr. Loose, a florist of Alexandria, Va., under the direction 
of Mr. A. F. Woods, of the Bureau of Plant Industry. The writer 
cooperated in so far that he examined the roots for nematodes after 
the experiment. The following extracts from Mr. Loose's report of 
the experiment indicate the methods used: 

In the early part of February a bed of Bridesmaids, 150 feet long and 3 feet wide, 
4 inches soil, was thoroughly saturated, using 50 gallons of the 1 per cent mixture. 
The plants did not seem to suffer from the application, and one week later we were 
able to see young healthy roots making their appearance, while the old fibrous roots 
were entirely decayed. We then treated in the same manner Bride, Kaiserine, 
Chatanays, Nephetos, Beauty, Liberty, and Meteor with equal success as to freeing 
the soil of the pest. 

Some strong-growing varieties, however, such as Beauties, Chatanays, and Kaiser- 
ine, suffered and lost much of their foliage. Even some of the soft growth wilted 
during the sunny part of the day. My experience in this treatment is that care 
should be taken to harden the plants by lower temperature and keeping the beds 
dry, being careful, however, to give the plant a good watering 12 hours before apply- 
ing the mixture. * * * The cut of roses on February 10, at the time when we 
applied the remedy, had dwindled down to 250 a day. It remained practically sta- 
tionary during the four following weeks. We were able, however, to notice that the 
foliage was regaining its normal color and the plants were starting strong growths. By 
April 1 our cut had increased to 500 daily, mostly prime stock, and by the middle of 
April it had resumed its normal cut of 1,000. 

As a matter of experiment we left a few plants untreated at the ends of some of the 
benches, and to-day, May 10, they are practically worthless, showing effectually that 
the spring weather had nothing to do with the improvement. The roots of the un- 
treated plants looked like a ball of fern roots used for orchid potting, full of galls and 
matted, plants making a weakly growth, foliage pale, and flowers insignificant. On 
the contrary, the plants treated last February have healthy strong roots, making fine 
growth and the foliage of the very best color. 
91294°— Bui. 217—11 4 



48 ROOT-KNOT AND ITS CONTROL. 

The mixture was applied with the hose connected to a force pump at the rate of 4 
pounds of formaldehyde to 50 gallons of water, the treating of 15,000 plants requiring 
200 pounds of formalin, worth about 18 cents a pound, making the treatment quite 
inexpensive considering the result. 

Since this experiment this method has been tried in a number of 
places and with success where the proper precautions were taken. 
Doubtless other plants might be treated similarly, but the method 
should be tried with caution, even for roses, until it is ascertained 
that the plants will not be killed. 

MISCELLANEOUS. 

Plants for which the formaldehyde treatment can not be used can 
often be benefited by the following treatment: Remove them from the 
soil, wash the roots clean, and cut away every diseased root, burning 
them. Top the plant to correspond with the amount removed from 
the roots and plant in nematode-free soil. Such severe treatment is 
too injurious to some plants, and about all that can be done then is to 
give them plenty of well-aerated soil with an abundance of fertilizer, so 
as to stimulate root growth to more than counterbalance the roots 
that are reduced in value by the entry of the nematodes into them. 

It is possible that by transplanting diseased plants to stiff clay soil 
the number of nematodes will be so reduced that a subsequent trans- 
plantation to more suitable soil will find them free from the disease. 

On purchasing rooted plants, unless they come from a place known 
to be free from root-knot, it will always be best to put them into a 
quarantine bench for several months. If at the expiration of this 
time they show no signs of the trouble, they can safely be removed to 
their permanent quarters. Of course the soil in the quarantine bed 
must be renewed whenever it becomes infested with the nematodes. 

Moderate quantities of soil can be freed from the pest by putting 
it at the beginning of winter in a place where it will be exposed to the 
cold and subject to drying out at the same time. Thus, it can be 
thrown upon boards in a comparatively thin layer. The boards will 
keep the nematodes from passing downward into the ground as the 
soil dries out. At the same time the boards keep the moisture from 
the soil beneath from passing by capillarity up into the soil from the 
beds. The continued drying and freezing, especially if the soil be 
occasionally stirred, is fairly effective in killing off the nematodes. 

CONTROL OF ROOT-KNOT IN THE FIELD ON PERENNIAL CROPS. 

The treatment of perennial crops in the field is of a greatly different 
nature from that of plants in the greenhouse, cold frame, or seed bed, 
for a process that could be applied with profit to such valuable soil 
as that in greenhouses, etc., might, indeed mostly does, prove too 

217 



CONTROL OF ROOT-KNOT. 49 

expensive for ordinary use in large fields where the crop value per 
given area is far lower. The methods to be applied differ according 
to whether the land is used for annual or short-lived crops or is pos- 
sessed by a long-lived crop, such, for example, as fruit trees. In the 
former case the treatment can be begun after the crop is off, while in 
the latter it must be of such a nature that the trees present do not 
receive injury. The latter problem will be discussed first. 

In the South the trees most generally affected seriously are the 
peach, fig, mulberry, and walnut, while in California and Arizona 
the Old World grapevine is seriously affected in addition. Many 
other plants are subject to great injury elsewhere, such as coffee in 
Biazil, Mexico, and the East Indies; papaya (Carica papaya) in 
Florida and the Tropics; shrubs like tea in Ceylon and India, etc. 
By consulting the list of plants subject to the disease it will be seen 
that many are woody plants and that of these a number besides those 
mentioned are seriously injured by the disease. 

CHEMICALS. 

Of the various treatments proposed, the use of chemicals has offered 
a wide field for investigation and one that is by no means thoroughly 
explored as yet. The more promising chemicals tested by the writer 
are mentioned in the following paragraphs : 

Carbon bisulphid. — This has been used in Europe for the phyl- 
loxera on vine roots where the plants were dormant, without serious 
injury to the vine. The writer's experiments, however, lead him to 
look upon it with suspicion. Many plants were very quickly killed 
by it and others seriously injured. Its use should not be attempted 
without first testing its effect upon one or two trees. These should 
preferably be dormant, at least not in an actively growing condition. 
The root hairs are killed outright, so the plant must not be where 
it will actively transpire until new root hairs are formed. The usual 
method of procedure is to make holes in the ground to a depth of 
several inches or a foot or more, the carbon bisulphid being poured 
or injected into these holes and the latter covered up with dirt before 
the liquid volatilizes. The fumes penetrate the soil and destroy 
nearly all living things. Extreme care must be used in handling 
this chemical, as its fumes are poisonous and exceedingly inflammable, 
being explosive when enough air is mixed with them. 

Carbon bisulphid will doubtless be of value in an orchard or grove 
where it is desired to replace certain trees or fill vacant places with 
new plants. By its use the spots where the old trees stood or where 
vacant places are to be filled can be thoroughly disinfected. After 
a week or two the trees can be set out and, the soil being free from 
nematodes, can make quite a start before the nematodes from the 

217 



50 BOOT-KNOT AND ITS CONTROL. 

soil outside of the disinfected patch can get to their roots. In deep 
sandy soil the writer found not all the nematodes destroyed by the 
use of 2 ounces of carbon bisulphid per square yard, but when 4 
ounces were used they were exterminated. The size of the area to 
be treated depends upon the size and rapidity of growth of the trees 
to be planted, the faster they grow the smaller being the area to be 
treated. For the best results the chemical must be placed at a depth 
of several inches below the surface, the opening being firmly closed 
so that the vapors will have to diffuse throughout the soil. In France 
special forms of apparatus have been devised for this purpose in 
combating phylloxera. They consist of a reservoir for the liquid and 
a hollow rod which can be inserted to any desired depth, a measured 
quantity of the liquid then being forced out into the soil. In the 
writer's experiments, however, use was not made of these rather 
expensive contrivances, but of a simple dibble consisting of a pointed 
piece of broomstick. Holes were made to the depth of a foot to the 
number of eight or nine to the square yard. The desired amount of 
carbon bisulphid was poured into them, each being closed at once by 
the foot and the earth firmly pressed down to prevent the escape of 
the vapors into the air. About a teaspoonful to each hole is sufficient, 
or about 4 ounces to the square yard. 

Potassium sulphocarbonate. — Potassium sulphocarbonate in the form 
of a solution of 1 part, by weight, to 5 parts of water to be applied in 
little trenches dug around the diseased trees is recommended by Gan- 
dara. 1 According to him, 4,000 liters of the solution suffice for a 
hectare — i. e., about 425 gallons per acre. His experiments were with 
nematode-affected coffee. This treatment he reports as being success- 
ful, but too expensive for general use. The writer's results, however, 
were not so successful. Papaya plants (Carica papaya), about 18 to 
20 months old and with roots badly affected with root-knot, were used. 
The chemical, diluted as directed by Gandara, was applied to some 
trees in little ditches and to some in numerous holes about a foot deep. 
After it had all soaked in, the soil was watered thoroughly, ^s it was 
very dry, so that the chemical might the better soak evenly through 
the soil. In a day or two some of the old leaves dropped, showing 
that the roots had suffered some injury; but at the expiration of a 
few weeks the roots were found to be as badly knotted as ever, prov- 
ing that for the papaya, at least, this process is ineffective. The 
high cost of the chemical, moreover, would make its use utterly 
impracticable. 

FormaldeJitjde. — In view of the comparative success obtained with 
formaldehyde solution on roses it was tested on papaya trees out of 
doors. A ridge of earth was made around each tree at a distance of 

iG&ndara,1906. 
217 



CONTROL OF ROOT-KNOT. 51 

about 5 feet, so as to retain the solution. One part of commercial 
formaldehyde (about 40 per cent strength) was mixed with 100 parts 
of water. About 25 gallons were applied to each tree — i. e., about 3 
gallons to the square yard. In some cases water was applied after- 
wards to cause the solution to penetrate deeper; in other cases no 
water was added. A few of the older leaves turned yellow and 
dropped off a day or two after the treatment, but no further injury 
was noticeable. In two weeks the nematode root galls, containing 
living nematodes, were found to be almost as numerous as ever, 
although a good many of the galls on the roots nearest the surface 
were found to contain dead nematodes. These and other experi- 
ments lead the writer to believe that where the soil is rather deep and 
the liquids applied can drain through instead of remaining in the 
immediate vicinity of the roots this formaldehyde treatment is not 
likely to prove very effective. 

Calcium carbid. — The use of calcium carbid was also recoin- 
mended by Gandara. 1 His instructions were to mix 4 parts of it 
with 1,000 parts of water. After letting it stand half an hour this 
milky solution is to be injected into the soil in five holes per square 
meter, 10 grams to a hole. Through lack of other trees suitable to 
test it on, papaya trees were also used in testing this method. A 
modification was also made in that about an ounce of the calcium 
carbid, without previous treatment with water, was placed in the 
bottom of 8-inch holes, which were promptly plugged with earth, 
about eight or ten holes being made to the square yard. Afterwards 
the soil was thoroughly watered. In this case a strong odor of acety- 
lene was noticeable for two days. No damage was done to the trees 
and the nematodes in the galls were not killed by either treatment. 

Other chemicals. — Various other chemicals recommended have the 
disadvantage that they are poisonous to living plants or too expen- 
sive. It is still possible, however, that some easily volatilizing liquid 
may be found whose vapors while fatal to the nematodes will not 
seriously injure the plants harboring them. Of those already men- 
tioned carbon bisulphid has many desirable qualities ; but its poison- 
ous effect on vegetation is against it. It is possible that by applying 
it only during the dormant season of the plant and carefully regulat- 
ing the quantity applied it may prove as effective as it is claimed by 
some investigators to be against phylloxera in the vine. The writer's 
experiments were mainly carried on at Miami, Fla., where there is 
no dormant season; hence this point could not be well determined. 
It is also conceivable that after a period of dry weather the chemical 
might be less harmful, as the trees would then be in a less actively 

i Gandara, 1906. 
217 



52 ROOT-KNOT AND ITS CONTROL.. 

growing condition and perhaps, therefore, less injured when the root 
hairs were killed by the chemical. Further experiments on this line 
should be carried out. 

FERTILIZERS. 

It is the result of general observation that if trees affected by root- 
knot can be forced into rapid growth, especially in the early part of 
the season, so that the roots penetrate deeply into the ground and 
form a widely branching system, they will thenceforward usually 
develop normally and cease to show much injury from the nematode. 
This is particularly the case with the peach. Many growers now on 
setting out an orchard where the pest is present fertilize the trees 
very highly, so that they may start right into growth and keep ahead 
of the nematode injury. As shown on page 41, the nematodes are 
mostly confined to the upper 12 to 16 inches of soil, so that if the 
roots can be forced to grow rapidly and deeply enough they will 
escape much injury. To accomplish this, it is necessary that the soil 
be prepared to a good depth before setting out the trees and that an 
abundance of nitrogenous fertilizers be given. The various potas- 
sium salts, too, are apparently very beneficial in the Southeastern 
States, so much so that some people believe that they destroy the 
root-knot nematode. Perhaps in the naturally rather potash-poor 
soils of many of the Southern States the addition of potassium is 
simply another factor in bringing the plant to its normal resistant 
power. At any rate, in the writer's experiments plants given an 
excess of potash suffered less from root-knot than those not so fer- 
tilized. It has been found in Germany that the sugar-beet nema- 
tode removes the mineral salts from the roots about equally. If, 
however, the soil is not much overstocked with potash it would be 
exhausted in the plant sooner than the others, for, being less abundant 
in the soil, it would be taken up less rapidly by the roots. The same 
would be true of any other of the necessary minerals. This may 
explain the effect of potash in combating this disease. 

FLOODING. 

In view of the fact that root-knot injury never seems to be severe 
in soils that are flooded for a part of each year it seemed reasonable 
to suppose that flooding might have a beneficial effect when applied 
to affected trees. Unfortunately, however, through a misunder- 
standing of instructions the experiments arranged to be carried out on 
this line failed to be performed. It is certain, however, that great 
care must be taken, for many trees are killed by having their roots 
submerged even a few days. 

217 



CONTROL OF ROOT-KNOT. 53 

CONTROL OF ROOT-KNOT IN THE FIELD WHEN NO CROP IS PRESENT. 

Land known to contain the root-knot nematode and not occupied 
by a permanent crop like an orchard, grove, etc., may be freed from 
the pest far more readily than land so occupied. The methods are 
the same, whether the land is to be planted subsequently to annual 
crops or to trees. The only difference is that land destined for 
perennial crops must be more thoroughly cleared of the root-knot 
nematode than that destined for simply one-year crops. 

CHEMICALS. 

Carbon bisulphid. — Carbon bisulphid is undoubtedly the most 
efficient chemical for the destruction of the nematode in fields. 
Experiments were made by the writer at Monetta, S. C, in 1906 and 
repeated in 1907, which showed that when used as previously described 
at the rate of 4 ounces per square yard of surface the nematodes were 
practically exterminated, being found only at the edges of the plats, 
where they could have come in from the surrounding untreated land. 
Two ounces per square yard did not prove so effective, although the 
nematodes were largely destroyed by even this application. In 
view, however, of the quantity required and of the high price of this 
chemical it is very evidently out of the question to apply it on a 
large scale. Even in bulk the crude carbon bisulphid costs 10 to 
15 cents a pound. At 4 ounces a square yard the cost for an acre, 
not including cost of the labor required, would be from $120 to $180. 
Nearly all the chemicals that have been suggested have the same 
fault. Yet for small patches when it is desired, perhaps, to destroy 
the nematode where a tree is to be set out, or in a small spot where 
the pest has appeared but has not spread badly, it would probably 
be found very effective. 

Formaldehyde. — Formaldehyde was tested at Monetta, S. C, in 
both 1906 and 1907, and at Miami, Fla., as well, in 1906. It was applied 
as a solution of 1 part commercial formaldehyde (36 to 40 per cent) 
in 100 or 200 parts of water. The solution was either sprinkled directly 
on the surface or poured into deep furrows, which were leveled off after 
the solution had soaked in. From 1 to 2 gallons per square yard of 
surface were used. As a whole, the treatment did not recommend 
itself. In no case were the nematodes entirely destroyed, although 
they were considerably reduced in numbers. The plants grown on 
these plats after the treatment showed the presence of root-knot 
galls on their deeper roots, although most of the upper layer of soil 
seemed to be free from the pest. This would indicate that a larger 
quantity would perhaps penetrate deeply enough to kill all the 
nematodes in the soil. With formaldehyde at 20 cents a pound, 
wholesale, the cost of treating an acre with the stronger solution, 

217 



54 ROOT-KNOT AND ITS CONTROL. 

2 gallons per square yard, would be about SI 50 exclusive of labor, 
which would include the hauling of 5,000 to 10,000 gallons of water. 

Calcium carbid. — At Monetta, S. C, experiments were made with 
calcium carbid. It was strewn in furrows which were then covered 
over so that the resulting acetylene gas should penetrate throughout 
the soil, or it was applied as a solution in water. The amount of root- 
knot was reduced, but in all cases where the reduction was great the 
injury to the crops, especially to tomatoes, was also great. Better 
results were obtained from the dry application in 2-inch furrows than 
from the solution. Planting was not undertaken for a week or two, 
but still the results were such that in spite of replanting a second and 
even a third time the test crops — okra, beans, tomatoes, and cowpeas — 
were badly killed out. The odor of acetylene was perceptible for sev- 
eral days. The fairly effective amounts were 1,500 pounds per acre, 
dry, in shallow furrows or a solution of 5 pounds per 100 gallons of 
water applied in deep furrows, 1 to 2 gallons per square yard. In 
view of the high cost of the treatment (at 10 cents a pound this would 
be $150 per acre exclusive of labor for the dry application and $25 to 
$50 for the solution) this method can not be recommended. The 
injury to vegetation is also against it. 

Potassium sulpJiocarbonate. — This salt is obtained commercially as 
a concentrated dark-brown solution, smelling strongly of sulphureted 
hydrogen. Gandara x states that it has been tried against phylloxera 
in France and recommends it for root-knot, at a rate of 1 part 
of potassium sulphocarbonate to 5 parts of water. Accordingly, the 
following experiments were outlined. Plats of land were laid off as 
follows: (1) Check, no treatment; (2) 10 parts of the chemical to 
90 parts of water, 2 quarts per square yard in holes which were quickly 
filled; (3) 1 part to 99 of water poured on the surface at a rate of 
2 gallons per square yard, that being the quantity necessary to wet 
the surface thoroughly; (4) a similar quantity of a solution of 1 part 
to 199 of water; (5) check. After a few days beans, tomatoes, okra, 
and cowpeas (New Era) were planted. In all cases where the 
chemical was used, both weak and strong, the tomatoes, okra, and 
beans were to a large extent killed, but the cowpeas were not hurt. 
Root-knot was present, however, even where the solution was the 
strongest. As a fungicide, too, this chemical had little value, for 
Rhizoctonia was very abundant at the crowns of all the plants. 

For field use, then, this chemical is not to be recommended as a 
means of combating the root-knot nematode. 

Ammonium sulphate. — Van Breda de Haan 2 recommended against 
the nematode on tobacco in the Dutch East Indies the use of am- 
monium sulphate followed by quicklime. The latter sets free the 

i Gandara, 1906. s Breda de Haan, 1905. 

217 



CONTROL OF ROOT-KNOT. 55 

ammonia, which that author supposed might have value in destroy- 
ing the pest. The writer's experiments at Monetta, S. C, were as 
follows: Plats of nematode-infested land 10 feet by 70 feet and 10 by 
140 feet were laid off, separated from one another by ditches 2 feet 
wide. The chemicals were scattered on the surface and worked in 
with a cultivator or hoe. The rate per acre of the applications is 
here given, not the actual quantity put on the particular plats. 
(1) Water-slaked lime (quicklime put in a hole in the damp earth and 
left several days until slaked to a powder) 2 tons per acre, ammonium 
sulphate 1 ton per acre; (2) quicklime 2 tons, ammonium sulphate 
1 ton; (3) slaked lime 2 tons; (4) quicklime 2 tons; (5) check. Sum- 
mer squashes were planted on one half of each plat and New Era 
cowpeas on the other half, both these crops being very susceptible to 
nematodes. 

Plats 3 and 4, respectively, slaked lime and quicklime, showed a 
very great abundance of root-knot, even more than plat 5, the check. 
The plants were pale in color and weak. Evidently lime in the 
quantities used is not effective against root-knot. In plats 1 and 2, 
ammonium sulphate plus slaked lime and quicklime, respectively, the 
squash roots were fairly badly knotted, especially in plat 1, but not 
nearly so badly as in plats 3 and 4 or in the check plat (5). The cow- 
peas were very dark green in color and very vigorous, and only moder- 
ately affected with root-knot, far less than plats 3 or 4, perhaps 
about like the check. The two plats with ammonium sulphate 
ripened their seed earlier than any other of the experimental plats. 
The next year these plats were again planted, this time to cowpeas, 
okra, tomatoes, and beans. The chemicals were not added, but 
observations were made to determine whether any beneficial effect 
might show the second year. The ammonium-sulphate plats were 
distinctly better than the check or those with lime alone, and were 
only moderately affected with root-knot, although by no means free 
from it. 

Experiments similar to these but on a very much smaller scale were 
made in Miami, Fla. Quicklime, even at the rate of 5 tons to the acre, 
did not suffice to prevent nematode injury, while root-knot was quite 
abundant in a plat treated with quicklime at the rate of 2 tons per acre 
with 2 tons per acre of ammonium sulphate dissolved and poured over 
the surface. 

We must then conclude that these chemicals are not of special value 
for the combating of nematodes. 

Abbey l recommends using siliconuorid of ammonium at the rate 
of 1 ounce to a square yard. It must not be applied to soil containing 
living plants, as it will kill them. It soon decomposes and then is 

i Abbey, 1898 and 1899. 
217 



56 ROOT-KNOT AND ITS CONTROL. 

harmless. Abbey also recommends 3 ounces of Little's soluble phenyl 
in 3 gallons of water applied around affected roots. Dyke 1 and 
Iggulden 2 also tried the latter, but Dyke found it a failure, claiming, 
however, that kainit was effective. 

FERTILIZERS. 

Closely related to the use of chemicals may be considered the effect 
of various fertilizers on the development of root-knot. At Monetta, 
S. C, the following fertilizers were tested in 1906, mostly in one- 
twentieth acre plats separated by ditches (or rather very deep furrows) 
2 feet wide, the numbers in parentheses referring to the field numbers 
of the plats: (12) Kainit, 1,000 pounds per acre; (13) ammonium sul- 
phate, 667 pounds per acre; (14) kainit, 500 pounds per acre; (15) 
high-grade potassium sulphate, 1,000 pounds per acre; (16) check; (17) 
high-grade potassium sulphate, 500 pounds per acre; (18) 17 per cent 
acid phosphate, 1,000 pounds per acre; (19) 17 per cent acid phosphate, 
1 ton per acre; (20) check. In 1907 the following tests were made: 
(1) Kainit, 1,000 pounds per acre; (2) kainit, 1,500 pounds per acre; 
(3) high-grade potassium sulphate, 667 pounds per acre; (4) high-grade 
potassium sulphate, 1,333 pounds per acre; (5) ammonium sulphate, 
1,000 pounds per acre; (6) muriate of potash, 1,000 pounds per acre; 
(7) potassium magnesium carbonate, 667 pounds per acre; (8) potas- 
sium magnesium carbonate, 1,333 pounds per acre. The checks 
received no numbers in 1907. The plats of that year and the checks 
were planted to tomatoes, okra, beans, and New Era cowpeas, all of 
which are very susceptible to root-knot. The last year's plats (1906 
experiments) were also replanted in 1907 with these four plants. In 
1906 the fertilizer plats were planted with New Era cowpeas and 
summer squashes. To all of the fields was applied each year, at the 
rate of 500 pounds per acre, a special brand of commercial fertilizer 
in common use in that vicinity, the soil being so poor that without 
some complete fertilizer nothing would grow well. The experiments 
were intended to show the effect, if any, of an excess of some par- 
ticular fertilizer over the normal quantity applied. 

The 1906 plats showed plainly the beneficial effects of potash fer- 
tilizers on the sandy soil of the experimental field. All the plats 
treated with kainit and potassium sulphate were darker green and the 
plants were far more vigorous than on the other plats. In fact, plats 
12 and 15, respectively, kainit and potassium sulphate, both 1,000 
pounds to the acre, were, so far as the cowpeas were concerned, hard 
to excel anywhere. The squashes did not show much difference in 
any of the plats. They were badly infested with the squash bug, 

i Dyke, 1897. J Iggulden, 1898. 

217 



CONTROL OF ROOT-KNOT. 57 

which killed the plants out in some of the plats. The cowpeas in 
plat 12 showed no nematodes and but few were present in the squashes. 
Plat 14 had a fair amount of root-knot in the cowpeas and from few 
to many on the different squash plants. The rest of the plats did 
not differ materially from the check plats which were fairly badly 
affected, in spots very badly. 

The plants grown on these same plats in 1907 without the addi- 
tion of the fertilizers again were badly affected except in plat 12, and 
somewhat in plat 15, which remained fairly free, showing a residual 
effect. 

In the 1907 fertilizer experiments the following results were 
obtained. The kainit applications were injurious to the germina- 
tion of the seeds, both the 1,000 as well as the 1,500 pound applica- 
tion, but naturally the latter more markedly. The amount of root- 
knot, however, in these plats was slight. Potassium sulphate at 667 
pounds per acre was not injurious, but at twice that amount it so 
injured the germination of the cowpeas and beans that they required 
replanting. Root-knot was fairly abundant and, strangely, more so 
in the more highly fertilized plat. In both plats the growth of the 
plants was very vigorous. The sulphate of ammonia at the rate used 
exerted a very harmful effect on germination, requiring several 
replantings. The plants that did grow, however, were very vigor- 
ous, dark green, and rather free from nematodes. The muriate of 
potash injured the germination of the beans and cowpeas, while the 
nematodes were fairly abundant. The potassium magnesium car- 
bonate gave the best and most vigorous plants of all, without injury 
to germination. Root-knot was present in most of the plants, but 
not abundant. 

Judging from these experiments, it is clear that fertilizers alone 
can not be depended upon to exterminate root-knot. On the other 
hand it is also plain that some fertilizers exert a beneficial effect upon 
the plant and enable it to make a good crop in spite of nematodes. 
Perhaps they may also increase the resisting power of the plant 
against the entrance of the nematodes into the roots. The potash 
fertilizers seem to be most favorable for this purpose, so far as the 
experiments at Monetta and observations elsewhere go. However, 
it will not be safe to conclude that they will be equally beneficial 
everywhere. In the sandy, rather potash-free soils of South Caro- 
lina and Florida the application of potash in amounts not too large 
seems to be followed by favorable results. 

According to Stift, 1 Hollrung, in Germany, has shown that ferti- 
lizing highly with potash alone is not of much benefit to beets attacked 
by the sugar-beet nematode. Wimmer has shown that the nema- 

i Stift, 1908. 
217 



58 ROOT-KNOT AND ITS CONTROL. 

todes remove the different minerals almost equally, so that only 
where one element is rather deficient will the addition of that alone 
be of benefit. The sugar-beet nematode removes large quantities 
of mineral food from the roots, so that unless these minerals are 
present in the soil in considerable excess over that naturally needed 
by the crop the plants will suffer from lack of that mineral which is 
not sufficiently superabundant. Thus, an amount of potash sufficient 
for a healthy crop may be insufficient if the sugar-beet nematode is 
present, and the symptoms of potash hunger can be averted only by 
applying an excess of potash. Probably this is also true of the root- 
knot nematode. The sandy soils of South Carolina are rather potash 
poor, so that a diseased plant will suffer from potash hunger, while 
the other elements may be in sufficient abundance. At any rate, 
the addition of potash in excess proved helpful. The nitrogen- 
containing fertilizers when not in too great excess also benefited the 
plants somewhat, but not so markedly as the potash. This is to be 
expected, as nitrogen is not any too abundant in those soils. The 
phosphatic fertilizers, however, showed no benefit at all. 

Caution must be taken not to apply too much potash. In 1907, 
in fact, kainit at 1,000 pounds per acre was harmful in that many of 
the young seedlings were killed, necessitating replanting several times 
in order to get a fair stand. This quantity was not harmful in 1906 
on another plat, showing that the danger limit is probably not far 
below that amount. Muriate of potash at the same rate was very 
harmful in 1907, as was also the same amount of ammonium sulphate. 
Potassium sulphate, 667 pounds to the acre, and potassium magnesium 
carbonate, 667 and 1,333 pounds to the acre, were absolutely harm- 
less, while the latter amount of potassium sulphate was only 
slightly harmful. 

In spite of the high fertilization a field continually planted to 
nematode-susceptible crops will, if the nematode is present, eventually 
become so infested with that parasite that it will be impossible to 
make paying crops. However, it can not be denied that for special 
occasions it is of value to reduce part of the evil effects of the nematode 
infestation by high fertilization. 

FLOODING. 

The objections to flooding the soil that would apply in the case of 
land occupied by permanent crops do not hold good in fields devoted 
to annual or short-period crops. In the former case the soil can not 
be kept submerged longer than a few days or the roots are killed. 
In the latter case, however, the fields can be flooded for as long a 
period as desired before the crops are planted. There is no doubt 
that under such conditions flooding has value. This has already 

217 



CONTROL. OF ROOT-KNOT. 59 

been mentioned, reference being made to the conditions in the Ever- 
glade islands, where the never submerged tops of the islands are full 
of root-knot and the annually submerged sides are free from it. The 
writer has records of fields in Georgia badly infested with the root- 
knot nematode that were free from the trouble after a spring freshet 
that kept the ground submerged several days. 

Apparently flooding, unless possibly of long duration, will not kill 
the nematodes inclosed within the root galls, so that if such knotted 
roots of perennial plants are present the flooding must be continued 
much longer. In Yuma, Ariz., under the writer's directions a field was 
flooded. It had once been a vineyard of Old World grapes, but these 
had become unprofitable owing to the ravages of the root-knot, and 
the vines had been cut down or pulled up. Many of the roots, however, 
were left in the ground. The next year the field was planted to melons. 
When the writer saw the field in May, 1907, the young cucumber 
and melon plants were dying from root-knot and the pest was found 
in the old living grape roots. The field was flooded the following 
winter, but root-knot was again prevalent the following spring, 
although apparently not so abundant. It seems likely that the vine 
roots may have harbored and saved from destruction many nema- 
todes, or perhaps the flooding was not continued long enough. That 
under some circumstances even three weeks is insufficient appears to 
be the conclusion to be drawn from an experiment performed at the 
writer's suggestion by a fruit grower and nurseryman in California. 
He kept submerged for three weeks his field of sandy alluvial soil 
which was badly infested by nematodes. Afterwards grape cuttings 
and peach seedlings were set out in it. The grapes (a resistant sort, 
Rupestris St. George) showed no root-knot, but the peaches became 
knotted. This period seems excessive in view of laboratory results, 
and is not entirely free from doubt as to other possible means of in- 
fection, yet, until disproved, three weeks should be regarded as not 
enough time to exterminate the nematode by flooding. 

It is of interest that flooding the soil is claimed by Stift 1 to be of no 
value against the closely related sugar-beet nematode. 

Flooding, then, can not be recommended as a certain means of ex- 
terminating root-knot under all circumstances. Probably the soil 
should be flooded at least 25 days; in the laboratory the nematode 
larvae usually succumbed much sooner when isolated and placed in 
water. Furthermore, no roots of perennial susceptible plants must be 
present. When water is expensive or means of flooding are not at 
hand, or when the soil is too porous, it will be out of the question to 
try this method. The subject is one, however, that needs further 
investigation. It will be of interest to call attention to the phenom- 

1 Stift, 1903. 
217 



60 ROOT-KNOT AND ITS CONTROL. 

enon often observed that a sloping field may have nematodes at its 
upper or middle portion and be free from them at the lower end where 
the soil is water-soaked part of the year. 



Laboratory experiments by the writer seem to show that the root- 
knot nematode can not withstand the drying out of the soil. Thus, 
two pots of badly infested earth, containing badly knotted plants, 
were allowed to remain without watering from June 4 to September 
22, 1908. The soil became very dry and dusty. It was then watered 
and seeds of susceptible plants were sown. These remained entirely 
free from root-knot. It is certain that the adults are killed by drying 
out, they being, indeed, very susceptible to injury of that kind. The 
foregoing experiments led the writer to the conclusion that thorough 
drying was fatal to larvae and eggs as well. This was strengthened 
by the observation that in his cross-inoculation work where carefully 
washed root-knot roots of various plants were planted in sterilized 
pots of soil and seeds of the desired plants sown in the pots, infection 
was obtained wherever the roots used were fresh, while whenever 
they were somewhat wilted, not even dry, no infection was obtainable. 
Frank 1 and Stone 2 were also of the opinion that drying out was fatal 
to these nematodes. 

On the other hand, there are several recorded observations which 
would seem to indicate that the opposite is true, at least sometimes. 
Thus, Goldi 3 dried the roots of coffee affected with root-knot, both in 
the sun and in the shade. After two months he wet them up and soon 
found, with the aid of the microscope, numerous nematode larvae, 
which he considered to be those of the root-knot nematode. A second 
case was as follows: Prof. P. H. Rolfs, of the Florida Agricultural 
Experiment Station, 4 kept some sandy soil in the laboratory for 10 
months. It became dry long before the expiration of that period. 
The soil was watered and tomato seeds were sown. The radicles of 
the seedlings became swollen and cedematous in a manner resembling 
the work of the root-knot nematode. No nematodes were found 
within the roots, but clinging to the outside were found nematodes 
which he identified as Heterodera radicicola. 

Goldi's conclusions may have been erroneous, for there are many 
nematodes, almost indistinguishable from Heterodera radicicola in the 
larval state, that endure drying out for long periods. If they were 
examined only with the microscope and not tested in connection with 
living plants on which they could be grown to maturity, it would be 
almost impossible to tell whether those seen by Goldi were the one or 
the other. Prof. Rolfs, on the other hand, is not likely to have made 

i Frank, 1885. 2 Stone, 1899. ' Goldi, 1892. « Rolfc, 1894. 

217 



CONTROL. OF ROOT-KNOT. 61 

a mistake of this nature, performing the experiment as he did. Still 
it is not certain that he had Heterodera radicicola unless he actually 
had the mature nematodes, but on this point he says nothing. There 
are some other nematodes besides this species that cause root galls, 
and it is barely possible that it may have been one of these, not the 
root-knot nematode that Prof. Rolfs had, since this latter species is 
rarely even partially external in the tomato. Yet with the confirma- 
tion of these reports by Dr. Cobb's observations, it can hardly be 
doubted that under some circumstances some of the root-knot 
nematodes may survive drying out of the soil. 

Whether the drying out of the soil kills all the root-knot larvae or 
not, there is no doubt that their activity ceases and there is no injury 
by them in fairly dry soils. In a letter to the writer, C. P. Lounsbury, 
entomologist of the Department of Agriculture of the Cape of Good 
Hope, states that the nematode occurs only in loose soils well sup- 
plied with moisture. Badly knotted grapevines set out in rather dry 
soil not only recovered, at least in part, but the nematodes did not 
spread to surrounding susceptible plants. Lavergne x in Chile, 
Gandara 2 in Mexico, and Huergo 3 in Argentina also point out that 
dry soils are unfavorable to the development of root-knot. The 
writer has repeatedly sought for these nematodes in susceptible plants 
in dry soil outside of but in close proximity to badly infested irrigated 
fields in the semiarid parts of the country, but without success. 

In view of the foregoing facts, it is probable that deep plowing, so as 
to loosen up the soil quite deeply without harrowing to pulverize it, 
would permit it to dry out sufficiently in a dry season to reduce 
greatly the injury from the pest. Of course, this is possible only 
where the climate is dry and the rainfall slight. In irrigated districts 
it could probably be carried on, such fields not being irrigated for 
some months after plowing. Of course this will not have much effect 
if underground seepage or rains keep the soil moist. Unfortunately 
the writer was unable to test the efficacy of this proposed method by 
direct experiment. It is a method that should be tested at the earliest 
opportunity in those regions where it can be carried out. 

TRAP CROPS. 

After Kiilm, the great German agriculturist, had demonstrated 4 
that the so-called Riibenmudigkeit (beet tiredness) of sugar-beet 
fields was due to a nematode, Heterodera schachtii, he devised 5 a 
method of reducing the injury based upon the principle of trapping the 
nematodes in some susceptible plant and destroying the latter before 
the larvas which had entered the roots had reached maturity. For his 
trap crop he used a sort of summer rape. This was sown closely and 

1 Lavergne, 1901. 2 Gandara, 1906. 3 Huergo, 1902, 1906. « Kiihn and Liebscher, 1880. 
* Kiihn, 1881, 1882, 1886-1, 1886-2, 1891. 
217 



62 ROOT-KNOT AND ITS CONTROL. 

when the plants had grown long enough so that the first nematodes 
that entered the roots were not yet mature but were in the nonmotile 
stage they were plowed up and either removed and destroyed or 
turned under with the tops down and roots up. The plants treated 
in the latter manner died quickly and the nematodes in the exposed 
roots died within a few hours. By repeating this process several 
times (three to five) in a season the number of nematodes was found 
to be so reduced that good crops could be grown again for several 
years. In using tliis method extreme care must be taken to plow 
under or remove the plants at the right time, for if left too long the 
nematodes will reach maturity in the roots and lay eggs, thus increas- 
ing instead of diminishing the number of nematodes in the soil. 

Frank * and others have also recommended this method for com- 
bating the root-knot nematodes. The writer has found no record of 
any such experiment having been tried. He made experiments on this 
line two different years at Monetta, S. C, but with no success. A 
badly infested field was separated from adjacent plats by a shallow 
ditch, 2 feet wide. The plat was sown very thickly to Whippoorwill 
cowpeas, a variety susceptible to root-knot. Roots from numerous 
plants were examined microscopically at short intervals to determine 
the stage at which the nematodes first entering the roots had become 
motionless and were approaching sexual maturity. At that stage 
the plants were destroyed, on one plat by plowing them under, on 
another by loosening the roots and removing and destro} r ing the 
plants, roots and all. The time necessary to reach that stage was 
found to be from 19 to 21 days after the sowing of the seed. As soon 
as the trap crop was removed or turned under, the soil was made ready 
and resown with cowpeas, the process being repeated. This was done 
until four or five crops of cowpeas had been removed in this manner. 
The next year through these plats and the check plat were planted 
rows of tomatoes, beans, okra, and New Era cowpeas. Some of these 
plants remained free, while some were slightly affected and some 
very badly affected by root-knot, no difference being noticeable be- 
tween the trap-crop plats and the check plats. This was true both in 
the experiments of 1906-7 and of 1907-8, which were conducted on 
another field. 

The cause of the failure of this method can not be that a sufficiently 
susceptible host plant was not chosen, for the variety of cowpea used 
is very susceptible. Furthermore, cowpeas had been grown fre- 
quently on that land, so that the nematodes were, so to say, accus- 
tomed to that crop. The period of growth allowed was carefully 
checked by microscopical examinations so as to avoid any chance of 
letting the development of the nematodes progress too far, for if that 

i Frank, 1885. 
217 



CONTROL OF ROOT-KNOT. 63 

were permitted and egg laying were started the number of nematodes 
would be increased instead of diminished. Probably such large num- 
bers were present that only a part entered the trap plants and were 
destroyed, enough remaining in the soil to infest badly the next year's 
crop. It is possible that some other crop would have done better, but 
it could not have been clover, as Frank suggested, for that did 
not do well where the experiments were being carried on. The 
requisites of a good trap plant are fairly cheap seed, great susceptibility 
to nematode attacks, a wide-spreading root system, and rapid growth. 
All these are possessed by the cowpea to a greater or less extent. 



It has been seriously proposed to use steam to destroy nematodes 
in the field in view of the success with its use in the greenhouse, cold 
frame, and seed bed. The writer has made no experiments along this 
line, owing to the expense of the undertaking. It is seriously to be 
doubted whether a large field, producing a crop selling at $25 to $50 
or even $100 net per acre, could be profitably piped for steam sterili- 
zation. Small fields isolated from danger of reinfection by deep 
ditches, water, stiff soil, or other obstacles and devoted to the inten- 
sive culture of some very remunerative crop might be so treated with 
profit. For a large field a very large boiler and many hundred feet 
of perforated pipe would be necessary to steam the soil by the green- 
house method. 

Several schemes for sterilizing the soil in a field by means of mov- 
able apparatus have been devised, some of which have proved 
effective under certain conditions. Thus, for combating the Thielavia 
root-rot of tobacco, Gilbert l recommends the inverted-pan method 
of steam sterilization. This was devised by Mr. A. D. Shamel, of 
the Bureau of Plant Industry, for sterilizing nematode-infested soils 
in Florida. The following description is taken from Gilbert's account : 

The apparatus consists of a galvanized-iron pan, 6 by 10 feet and 6 inches deep, 
which is inverted over the soil to be sterilized and the steam admitted under pressure. 
The pan is supplied with steam hose connections, has sharp edges, which are forced 
into the soil on all sides to prevent the escape of steam, and is fitted with handles for 
moving it from place to place, the weight of the entire pan being not over 400 pounds. 
The soil is prepared as in the greenhouse method, a few potatoes being buried at a 
depth of a foot to gauge the degree of heat attained. A soil thermometer may also be 
used if desired. The steam should be kept at as high a degree of pressure as possible, 
80 to 100 pounds being best, and the treatment should continue for one to two hours, 
depending on the pressure maintained. In experiments conducted in the spring of 
1907, one hour's steaming at 80° C. under 100 pounds pressure gave best results in 
killing both the fungus and the weed seeds. When one section of the bed is treated, 
the pan is lifted and carried to an unsterilized portion and the operation repeated 
until the entire bed is steamed. 

1 Gilbert, 1909, pp. 35-36. 
91294°— Bui. 217—11 5 



64 ROOT-KNOT AND ITS CONTROL. 

The great objection to this method, and one that makes it imprac- 
ticable except for use on small spots, is the smallness of the area that 
can be treated at one time. Even with a pan of twice the area of that 
described, and allowing only one hour's sterilization each time, it 
would require more than 15 days, working da} 7 and night, to sterilize 
the soil on one acre of land. Furthermore, for deep soils, where, as 
already explained, the nematode sometimes is present at a depth of 
more than a yard, it is extremely doubtful whether the steam would 
penetrate deeply enough to destroy all the nematodes. This last 
objection applies to all methods of sterilization where an attempt is 
made to kill the nematode by heat or poisons. 



It is self-evident that if a field be kept free from all vegetation for a 
long enough period all the plant-parasitic nematodes within the soil 
will die from starvation. This is the principle involved in the use of 
the bare fallow. The field is plowed and kept free from weeds and 
other plants by frequent cultivation. In those localities where the 
winter is cold enough to prevent the further development of the 
nematodes during that period, it does no harm if grass or weeds grow 
up after the weather has become decidedly cool. This date might 
safely be put at November 1 for North Carolina, South Carolina, 
northern Georgia, Alabama, Mississippi, northern Louisiana, and 
northern Texas. In central and southern Florida and probably the 
southern portion of Texas and Louisiana, however, the nematode is 
active the year around, so that it would be necessary to keep the 
ground bare the whole time until the nematodes had died. In the 
early spring, where vegetation was allowed to grow in the winter, 
the cultivating to keep down the weeds must be taken up again before 
the soil begins to warm up. The length of time necessary to remain 
in fallow is not certainly known. Mr. A. D. Jackson, of Denison, 
Tex., found that 15 months in fallow was not sufficient to rid a field 
of root-knot nematodes entirely, although the number was greatly 
diminished. On the other hand, two whole years seem to be amply 
sufficient. 

This method has some objections which make it impossible to use 
in some localities. The land is idle and not only not productive, but 
requires the expenditure of time and labor to keep the vegetation 
down. Furthermore, the light soils where the nematodes abound 
are easily leached out when there is not a covering of vegetation. 
Then, such soils are subject to bad washing during heavy rains when 
they have no plant roots to bind them in place. A further objection 
is the destruction of humus in the soil exposed directly to the action 
of the fierce summer sun. The use of this method therefore can not 
be universal, although it is successful where it can be put into effect. 

217 



CONTROL OF ROOT-KNOT. 



65 



NONSUSCEPTIBLE CROPS. 

The most promising method, and the one that has given the best 
results wherever carefully tried, is that of growing crops that are not 
subject to root- knot until the nematodes causing the disease are starved 
out. To carry out this method successfully several things are requi- 
site: (1) The crops planted must be free from nematode attack, so 
that the larvae in the soil may not be able to find any nourishment 
to sustain their life and enable them to undergo their development. 
(2) The crop grown should at least pay the expense of working the 
land, as well as the rent, taxes, etc. (3) At the same time, if possible, 
the crops should enrich the land, or at least not impoverish it. (4) 
The plants must make such a vigorous, dense growth as to choke out 
all weeds or other plants that might harbor nematodes and permit 
them to develop and produce their numerous eggs. 

On referring to the list of susceptible plants it will be seen that with 
few exceptions none of the ordinary farm crops fulfill the first require- 
ment. However, the following plants appear to be free from nematode 
attack, at least under most conditions: Cowpea (the Iron variety), all 
species tested of Stizolobium (the velvet bean and close relatives), 
Florida beggarweed {Meibomia mollis), peanut {Arachis hypogaea), 
rye (Secale cereale), most varieties of winter oats (A vena sativa), crab- 
grass (Syntherisma sanguinalis), and possibly a few others. Webber 
and Orton * first called attention to the nematode-resistant quality of 
the Iron cowpea and recommended its use in combating root-knot. 
The velvet bean and beggarweed have been recommended by Rolfs, 2 
of the Florida Agricultural Experiment Station, who has also pointed 
out the value of crab-grass in a plan of rotation for reducing the num- 
ber of nematodes. Thus, he found the nematodes far less abundant 
the next year after an infested field was allowed to grow up to crab- 
grass for one year. 

The following rotations were planned by the writer for his work at 
Monetta, S. C, there being four plats measuring, respectively, 0.152, 
0.217, 0.217, and 0.166 acre: 

Table III. — Rotation of crops planned for four experimental plats at Monetta, S. C. 



Season. 


Plat 1. 


Plat 2. 


Plat 3. 


Plat 4. 




Beggarweed 


Velvet bean 


Virginia winter oats. . . 


Virginia winter oats. 
Beggarweed. 


Summer 







This experiment was planned for three years. It was begun in the 
fall of 1905. It was planned to keep careful records of all yields, etc., 
but in some cases the records are lacking. Unfortunately, the soil 



i Webber and Orton, 1902. 



» Rolfs, 1898. 



217 



66 ROOT-KNOT AND ITS CONTROL. 

proved so very poor for the oats that for it was substituted Abruzzes 
rye in succeeding years. Once each year the land was fertilized with 
the special commercial fertilizer previously mentioned at the rate of 
500 pounds per acre. 

The grain was harvested when mature, thrashed, and measured. 
As soon as the land could be put into proper condition the beggarweed 
and velvet bean seed were sown. In October a measured part of each 
field was carefully mowed and the vines cured to hay and weighed, thus 
permitting an approximate estimate of the actual yield per acre. The 
grain was sown as soon as the hay crop was cut and the land prepared. 
Unfortunately it was impossible, in addition to the substitution of rye 
for oats, to carry out the rotation just as planned, for in 1907 the beg- 
garweed seed obtained germinated so poorly that those plats were 
resown to velvet beans, as it was then impossible to get good beggar- 
weed seed. 

In the summer of 1908 across the south edge of the field rows of 
tomatoes, beans, okra, and New Era cowpeas were planted to test the 
degree to which the nematode infestation had been reduced by two 
years of these rotations. In the spring of 1909 another strip was 
sown to the same four kinds of plants, the remainder being planted with 
two varieties of cotton, viz, Triumph and Columbia. A similar area 
to the north of the rotation fields was also sown to the same sorts of 
cotton, while to the east was a field of Peterkin cotton belonging to a 
renter and not planted with reference to the experiment. The choice 
of the field to the north was made through an unfortunate misunder- 
standing. It was not discovered until the planting was done and the 
plants above the ground that that field too had undergone somewhat 
of a rotation, viz, 1906, cotton; summer of 1907, Iron cowpea; winter 
of 1907-8, rye; summer of 1908, Iron cowpea; winter of 1908-9, rye. 
The field to the east, which was sown to Peterkin cotton, was in cotton 
for the third successive season. 

The experiments were further interfered with by torrential rains 
which were harmful in two particulars, viz, they washed out much of 
the cotton and brought soil from nematode-infested fields and depos- 
ited it on parts of the rotation plats. 

217 



CONTROL OF ROOT-KNOT. 

The yields on the plats were as follows : 

Table IV. — Yield of crops on four experimental plats at Monetta, S. C. 



67 



Season and year. 



Crop. 



Actual yield. 



Yield 
per acre. 



Spring of 1906. 

Fall of 1906... 
Spring of 1907. 
Fall of 1907... 
Spring of 1908. 
Fall of 1908... 
Spring of 1909. 



/Oats bushels. 

\Rve do . . . 

(Velvet bean hay pounds. 

\Beggarweed hay do. . . 

Rye". bushels. 

/Velvet bean hay on own plat pounds. 

(.Velvet bean hay sown late on beggarweed plat . . .do. . . 

Rye bushels 1 . 

/Velvet 1 lean hay pounds. 

\Be;igarweed hav do. . . 

R ye s : 



About 4,900 
About 1, 575 

10J 
About 1,600 
About 730 

10i 
About 3,840 
About 560 



5.42 

11.300 

5,000 

14 

3,700 

2, 300 

14 

8,850 

1,770 



i 20J bushels on H acres; therefore estimated at 10} bushels for that field, 0.752 acre. 
2 Cut before ripening to allow cotton to be planted. 

At the prices current at Monetta, S. C, for hay (about $18 per ton) 
and grain (S3 per bushel in 1909 for seed, but here estimated at $1 per 
bushel) the value of the hay produced in the three years amounted to 
about $117 and that of the grain to $22.50, a total of $139.50, at the 
rate per acre of $156, $30, and $186, respectively, an average of $62 
per acre per year. While these yields are probably considerably more 
than enough to pay for working the land and the rent of the land 
besides, as well as payment for the seed, velvet beans having cost about 
$4 per bushel, it must not be concluded that the experiment was a 
failure in that the yields were not greater, for the primary purpose of 
the rotation was to reduce the nematode infestation while improving 
the land, or at least keeping it from deteriorating, and yet to make 
enough money to pay for the labor and seed used. 

To test to what extent, if any, the land was improved was the pur- 
pose of planting a plat of cotton at the north of the rotation plat. 
Unfortunately, so many plants in each section were washed out by the 
heavy rains that a very poor stand was obtained, with the result that 
the yield per acre on the rotation and check plats could not be deter- 
mined. The yields of the unginned cotton on the rotation plat were at 
the rate of 1 pound of cotton for 6 plants of Triumph and 6.1 plants of 
Columbia, while on the control plat to the north it took 6.9 and 7.25 
plants, respectively, to make a pound. The Peterkin plants to the 
east were not half as large and yielded even less. 

The soil which at the beginning was very poor in humus, so poor 
in fact that the rye would scarcely grow and the oats did not pay for 
cutting, gave a much better appearing field of rye the following 
years. The foliage of the cotton on it had a good color, showing that 
the leguminous crops had increased the nitrogenous content of the 
soil. 

217 



68 ROOT-KNOT AND ITS CONTROL. 

From the standpoint of nematode extermination the results were 
very satisfactory. Both in 1908, after two years of this rotation, 
and in 1909, after three years, the susceptible plants on part of the 
plat remained free from root-knot except as specified below. These 
plants were, as in previous tests, tomatoes, okra, beans, and New 
Era cowpeas, all extremely susceptible to root-knot attacks. Sev- 
eral rows of each were planted in 1908 along the southern edge of 
the plat, and in 1909 on the part just adjacent to that on the southern 
part of that portion of the field which had had a rotation of three 
years. Every plant was carefully dug up and all its roots examined 
after freeing them from the adhering soil. Every such plant was 
recorded as free, slightly affected, or seriously affected, a separate 
record being kept of all the plants in each hill. 

The field slopes very gradually toward the south from higher, 
somewhat nematode-infested land on the north. Two slight de- 
pressions lead somewhat diagonally from the northwest to the south- 
east. In the spring of 1908 and again in the early summer of 1909 
Monetta was visited by torrential rains which flooded and very badly 
washed the fields. Considerable soil from the fields to the north, 
and especially the badly infested field to the west, was washed down 
these depressions, settling on them and in the lower (southern) edge 
of the rotation field. Where these deposits of dirt occurred, and con- 
fined to these areas, some of the plants showed more or less nematode 
injury, most near the middle and least along the edges of the depres- 
sions. Furthermore, a few plants at the edges of the field, i. e., at 
the east and west ends of the rows, showed nematodes where they 
were probably introduced from the adjoining land in cultivating, 
plowing, etc. All the rest of the plants remained nematode free, 
although this field was badly infested before the experiment began. 

In accordance with suggestions of the writer, Mr. A. D. Jackson, 
of Denison, Tex., made some rather similar experiments, using Iron 
cowpeas and rye as his rotation. Certain fields were very badly 
infested, so badly, indeed, that the crops on them were almost a 
total failure. By growing the cowpeas two seasons with rye as the 
winter crop the nematodes were so reduced in number that only 
20 hills of cantaloupes out of half an acre were affected with root- 
knot and the crop of melons was excellent. Under date of July 
10, 1909, Mr. Jackson wrote as follows: 

I am well pleased with the Iron pea. While I have not eradicated the pest entirely 
by growing the pea two seasons, I have enriched my soil, have grown a large crop of 
feed, and the succeeding crop of vegetables has not in any case been materially af- 
fected (by nematodes). 

In Mr. Jackson's fields the writer's and Mr. Jackson's conclusions 
were that the few nematodes surviving were those that were pro- 

217 



FREEING A FIELD FROM ROOT-KNOT. 69 

duced on the few weeds whose presence it was impossible absolutely 
to prevent in the cowpeas. Thus, the weed known as careless weed 
(Amaranthus sp.) was found to have root-knot in the field of Iron 
cowpeas the second season these were grown. 

Mr. Jackson also made the experiment of using summer fallow in 
combination with winter rye, as follows: The preceding crop was 
taken off the summer of 1906, being badly knotted. The field was 
then kept in bare fallow from August, 1906, until the fall of 1907, 
when it was sown to rye. This was turned under when about mature, 
and in July, 1908, the field was sown to tomatoes (which are especially 
susceptible to root-knot). A fine crop of tomatoes resulted, the 
only nematodes present being in a small part of the field where Irish 
potatoes were badly attacked in 1906 and where volunteer potatoes 
came up in 1907. The remainder of the field remained free the 
succeeding year also (1909). 

Prof. P. H. Rolfs 1 recommends letting the field grow up to crab- 
grass (Syntlierisma sanguinalis) after the crops are removed, first 
taking up and burning or otherwise destroying the plants to avoid 
infection from them. According to him this method when used even 
for only one year greatly reduces the number of nematodes present. 
Dr. Neal 2 recommended the use of beggarweed, Japan clover, or 
Mexican clover. Regarding the latter the present writer knows 
nothing, but the first two are practically, if not entirely, immune 
and so ought to be valuable for this purpose. 

This method was used with complete success by Schroeder 3 in 
Germany against the stem nematode (Tylenchus dipsaci) after all 
other practicable methods had failed. He planted infected fields for 
a series of years with crops not susceptible to the nematode. After 
this period the fields gave again their normal yields of susceptible 
plants. 

RECOMMENDATIONS FOR FREEING A FIELD FROM ROOT-KNOT. 

In view of the results of the experiments described, the writer 
would make the following recommendations for freeing a field from 
root-knot. If the situation is one where the winters are cold and 
cool weather sets in in October, it will not be necessary to give 
attention to the subject during the fall and winter or in the spring 
before the ground begins to warm up. Under such conditions it 
would probably suffice to plow the land in the autumn, so as to have 
it in good condition for as early planting as possible in the spring. 
In the spring the field should be kept free from vegetation by cultiva- 
tion or harrowing until the ground is warm enough to' plant cowpeas. 
The field should then be planted thickly with Iron cowpeas, this 

i Rolfs, 1898. 2 Neal, 1889. * Schroeder, 1902. 

217 



70 ROOT-KNOT AND ITS CONTROL. 

variety being usually sufficiently resistant to the root-knot to permit 
its use for this purpose. In the fall this can be cut for seed or hay. 
The ground should then be plowed up and the process repeated the 
next season. Except in exceedingly bad infestations, two seasons 
devoted to Iron cowpeas should be sufficient to free the land from the 
pest. If desired, some winter grain, preferably rye or perhaps wheat, 
may be sown in the fall, the cowpeas not being planted until the crop 
is harvested early the next summer, following them by grain again. 
Where the weather remains warm rather late in the fall it would be 
desirable always to do this and so prevent the growth of weeds 
which might harbor the nematode in the fall and winter. Where 
the summer is long enough, velvet beans or Florida beggarweed are 
perhaps preferable to cowpeas, as they give a denser growth that more 
completely smothers out all weeds. Special care must be taken that 
in the summer time no weeds are allowed to grow in the field, as it 
will be seen by reference to the list of susceptible plants that many 
of the common weeds harbor the nematode. Their presence in the 
field, therefore, would serve to perpetuate rather than kill the 
nematode. 

Where practicable, the surest results can be attained by keeping 
the ground absolutely bare of all vegetation for two years. Tins can 
not be done on some soils, owing to the danger of the destruction of 
humus by the hot sun or of washing by heavy rain. 

Where the field is free from roots of perennial plants which might 
shelter the pest and is so situated that it can be submerged easily 
for long periods, it may pay to flood the land for three or four weeks, or 
perhaps during the winter. This would be impracticable except in a 
few locations. Furthermore, in many soils it would leach out all the 
plant food and make the soil poor, but where an impermeable layer 
will hold the water and keep it from leaching out it is conceivable 
that this method might be found very satisfactory. A short period 
of flooding or attempting to do this while the soil contains perennial 
roots containing the nematode will hardly prove successful. 

In the irrigated districts of the West, special care should be taken 
to avoid the introduction of this nematode into lands devoted to 
potato raising. To this end only perfectly sound, clean potatoes 
should be used; no potatoes from suspected regions should be planted, 
even should the individual potatoes appear perfectly healthy, with- 
out a preliminary sterilization with formaldehyde solution to destroy 
any nematodes present in the adhering soil. 

Should none of the foregoing methods be feasible, high fertiliza- 
tion, especially with that element (potassium calcium or phos- 
phorus) which is most nearly deficient in the soil, will prove helpful, 
although it will not kill the nematodes. When, as is often the case in 

217 



BREEDING STRAINS RESISTANT TO ROOT-KNOT. 71 

the sandy soils of the southern United States, the soils are already- 
deficient in potash, rather strong applications of some of the potash 
fertilizers — for example, kainit, potassium magnesium carbonate, 
sulphate of potash, etc. — are very helpful. Care should be taken 
not to apply enough to prevent the germination of the seed. 

BREEDING STRAINS RESISTANT TO ROOT-KNOT. 

As already mentioned, Webber and Orton have shown * that the 
Iron variety of cowpea is practically immune to root-knot and wilt 
(Neocosmospora vasinfecta), while most other sorts are exceedingly 
susceptible to both diseases. The latter investigator has continued 
his breeding experiments, using the Iron cowpea as one of the parents, 
and has produced several varieties more prolific than that sort in 
which the resistant characteristics are present. Similarly in the 
breeding of tobacco, Shamel and Cobey 2 obtained a strain resistant to 
nematodes. Certain sorts of figs — for example, Celeste and Pou- 
lette — are said to be less subject to injury by nematodes than other 
kinds. Among grapes, so far as the writer's observations go, the 
Old World species (Vitis vinifera) seems to be especially liable to 
injury by root-knot, although the different sorts vary greatly in their 
susceptibility. Thus, Zinfandel and Muscat appear very subject to 
this trouble, while Sultanina (erroneously palled Thompson Seedless) 
is apparently not so easily injured. Some of the phylloxera-resistant 
hybrids and pure American sorts are practically immune to root- 
knot as well as to phylloxera, although some American sorts are quite 
badly affected by the nematode. These observations of the writer 
are confirmed by Lavergne, who states 3 that the European varieties 
are very susceptible to Anguillula vialae, as he calls the root-knot 
nematode, while those of American origin that are resistant to 
phylloxera are also resistant to root-knot. Of the watermelon- 
citron hybrids bred by Mr. Orton with resistance to wilt as the main 
aim, it was found by the writer that of one strain only 4 out of 333 
plants showed root-knot, i. e., 1.2 per cent, while in two other strains 
28 and 51.9 per cent, respectively, showed root-knot. The presence 
of such marked differences shows that it would be entirely feasible 
to breed a watermelon variety that would be practically immune to 
root-knot as well as to wilt. Bouquet de la Grye 4 points out that 
Coffea liberica is less susceptible to root-knot than C. arabica and 
recommends grafting the latter upon the former. To obtain a firm 
union, this must be done b} r an approach graft with seedlings. 

Simple selection can be and ought to be practiced by everyone who 
grows his own seed; more complicated breeding work, unless per- 

i Webber and Orton, 1902. 2 Shamel and Cobey, 1907. 3 Lavergne, 1901. * Bouquet de la Grye, 1899. 
217 



72 ROOT-KNOT AND ITS CONTROL. 

formed by men who can devote considerable time to it, hardly pays 
for the time and expense required. 

In carrying out simple selection we must remember that no new 
characters are originated by this method. We simply select and 
strive to fix in one strain certain characters that are present as 
variations in the plants we are working with. Thus, if we find in a 
field badly infested with nematodes that a certain proportion of the 
plants are free from root-knot while the rest succumb, it would 
probably pay to begin selecting seed from the unaffected plants. It 
is better still if we can inbreed or intercross similar resistant plants. 
On the other hand, resistance to nematodes seems sometimes not to 
be one of the variations occurring in a plant. Such a plant can not 
be selected, as there is no foundation on which to build. However, by 
crossing it with some nearly related nonsusceptible sorts, some of the 
progeny may possibly show desirable qualities of resistance while at 
the same time preserving the best qualities of the parent sorts. 

In all such breeding it must be borne in mind as a very important 
principle that this work should be done in badly infested fields. If 
naturally infested fields are not available, provision should be made to 
do this work where the disease is abundant. 

No attempt will be made here to describe the methods of selection 
or hybridization. These are known to all seed growers and breeders. 
They can be found described in detail in many publications. 1 

Every farmer ought to be able at least to carry on this simple 
selection : When any plants in an infested field show special vigor and 
freedom from root-knot they should be marked and the seed collected 
before the main crop is gathered. This should only be done, how- 
ever, if these resistant plants are also up to standard in all other 
features. 

SUMMARY. 

(1) The disease known as root-knot, characterized by enlargements 
of the roots and often leading to the death of the plant affected, is 
caused by a nematode (Heterodera radicicola (Greef) Mull.). This 
was probably originally native in the Tropics (of the Old World ?), 
but has spread into nearly every part of both Temperate Zones. 

(2) The plants recorded as more or less subject to attack number 
almost 480 species and varieties, including nearly all of the larger 
families of flowering plants. Probably many more are actually 
susceptible, but have not been reported yet as hosts. Most of the 
important field and garden crops and ornamental plants are more 
or less subject to root-knot. 

i Hays, 1901; Bailey, 1906; Orton, 1909; Reed, 1909; Salmon, 1907; Spillman, 1909; Wilcox, 1903; Oliver, 
1910. 

217 



SUMMARY. 73 

(3) The life cycle of this nematode, from egg to egg, may take place 
in four weeks, or longer, depending upon the temperature of the soil. 
The larval stage is that in which entry into the host takes place. 
It then becomes motionless and soon enlarges and undergoes a sort 
of metamorphosis, the males eventually recovering the original 
worm shape, while the females become pear or flask shaped and very 
much enlarged in their transverse dimensions. Each female lays 
500 or more eggs. The winter is passed probably most frequently 
in the larval stage in the soil, but in the case of galls on perennial 
roots the nematodes may overwinter in these in a more advanced 
stage, even as practically mature and perhaps already fertilized 
females. 

(4) For the rapid multiplication of the root-knot nematode the 
following conditions are necessary: (a) A certain degree of warmth 
of the soil. Thus, in southern Florida this nematode is active the 
year round, in part of South Carolina the active season is from 
April 20 or May 1 to the middle or end of October, while farther 
north the period is still shorter. (b) Loose-textured soil. Only 
sandy or at least light soil is favorable to its spread, (c) Moisture. 
The drying out of the soil is frequently fatal to the nematode and in 
any case prevents it from doing any harm. Apparently the moister 
the soil as long as it is well supplied with air, the more favorable it 
is to the nematode's development. However, wet soil, i. e., soil in 
which the air spaces are filled with water, is at length fatal to the 
nematode, (d) Food supply. The larvae are able to exist in the soil 
for more than one year, but apparently not for two years, without 
the presence of living plants into which to enter. They are apparently 
unable to develop beyond the larval stage unless they enter a suitable 
host plant. 

(5) The nematode is distributed in several ways: (a) The 
larvse move through the soil by their own motion, but the distance 
traversed thus is probably not more than 6 feet or so a season. 

(b) They are carried from field to field hi the earth clinging to imple- 
ments, the hoofs of animals, the shoes of laborers, wagon wheels, etc. 

(c) They are conveyed in the soil that is washed from one field to 
another by heavy rains, a very common mode of distribution of this 
pest, id) It is possible that heavy winds may carry larvse or eggs with 
the soil blown from one field to another, but probably most would be so 
dried out in the process that this is not much to be feared, (e) They 
are introduced into new places in the roots or in the dirt adhering to 
the roots of nursery stock, in rooted cuttings, potted plants, etc., 
especially those of the peach, grape, fig, mulberry, potato, ginseng, 
etc.; also in the dirt in which some seeds are packed. (/) They are 

217 



74 ROOT-KNOT AND ITS CONTROL. 

sometimes brought to a field in manure if the manure pile has stood 
on infested soil. 

(6) The following methods of control in greenhouses and seed beds 
may be used : (a) The most efficient method is the use of live steam 
at fairly high pressure. The steam is forced through a system of per- 
forated pipes laid at the bottom of the bed or bench, (b) The old 
infested soil may be entirely removed and the benches thoroughly 
cleaned out. Then noninfected soil may be put in its place. This 
method is not advisable in regions where the nematode occurs out 
of doors in the vicinity, (c) Infected soil, when it is desired to save 
it and steaming is impracticable, may be freed by allowing it to he 
through the winter in a place where it will be exposed to alternate 
freezing and thawing, and especially to drying, (d) Soil containing 
perennial plants can be nearly if not quite freed from nematodes by 
the use of an abundance of a solution of formaldehyde (1 part of com- 
mercial formaldehyde to 100 parts of water). This solution is fatal 
to many plants and can be used only with great caution. 

(7) For the control of the nematode in the field where the land is 
occupied by perennial crops no entirely satisfactory chemical applica- 
tion can be recommended. Places where trees are to be reset should 
be freed from nematodes by the use of carbon bisulphid at a rate of 
3 or 4 ounces per square yard placed in about nine holes per square 
yard, these holes being about 6 to 12 inches deep and to be filled with 
dirt as soon as the chemical is placed in them. Carbon bisulphid can 
not be used with safety around living trees. Flooding the land seems 
to be unsatisfactory, as flooding long enough to kill the nematodes 
is usually fatal to the trees. High fertilization and constant culti- 
vation to induce growth often so help the trees that they are able, as 
it seems, to outgrow the trouble, the roots either penetrating to 
levels where the nematodes are less abundant or being formed faster 
than the galls can be produced. Avoid growing susceptible cover 
crops, like the ordinary nonresistant varieties of cowpeas, for exam- 
ple, for these multiply the nematodes in the soil manyfold. In pre- 
paring the land for setting out a perennial crop the soil should be 
freed from nematodes by the use of the methods suggested below. 

(8) For land infested with nematodes and not bearing a perennial 
crop, the following methods may be recommended: (a) Keeping 
the land free from vegetation of all kinds for two years. This is 
the most effective method, but it is not practicable in many cases. 
(&) Planting the land to nonsusceptible crops for at least two (perhaps 
better three) years, using in the winter small grains, such as wheat, 
rye, or oats, and in the summer the velvet bean, Florida beggarweed, 
the Iron cowpea, or even peanuts, scrupulously destroying all weeds 
that might harbor the nematodes, (c) Making heavy applications of 

217 



SUMMAKY. 75 

fertilizers, especially those containing potash, except where the soil 
already contains this in abundance. This treatment often reduces 
nematode injury greatly, (d) Flooding the land for a period of 
some weeks, (e) Where rain is not likely to interfere, plowing and 
allowing the soil to dry out for several months. (/) Preventing, by 
the use of embankments, ditches, etc., the washing of soil from infested 
fields to the field which it is desired to free from the pest. The intro- 
duction of the pest by tools, wagons, farm animals, etc., should be 
avoided. The trap-crop methods and the use of various chemicals 
have not proved practicable as tested by the writer. The former 
needs, perhaps, further trial. 

(9) The ideal procedure is to develop nonsusceptible strains of 
plants, so that the expense and trouble of exterminating the pest 
may be avoided. Such strains may be obtained by the selection 
of more resistant plants or by crossing with resistant strains followed 
by the careful selection and breeding of the progeny. 

Note. — While this bulletin was in press, there appeared a note in 
Science, 1 by L. N. Hawkins, describing the occurrence of Heterodera 
radicicola in the roots of Typha lalifolia near Ithaca, N. Y. 

The writer has just received from Mr. G. L. Fawcett, plant patholo- 
gist of the Porto Rico Experiment Station, Mayaguez, P. R., speci- 
mens of the bark near the base of a 15-year-old coffee tree. Mr. 
Fawcett writes: "The disease is characterized by a roughening of the 
bark at the base of the coffee tree, extending from the surface of 
the soil upward for a foot or two. No doubt it injures the tree, but 
such injury must be slight. I have seen no sick tree the bad condi- 
tion of which could clearly be ascribed to this nematode; only a 
small percentage of the trees in any plantation are infested. It is 
perhaps more common in moister and more shady places. Older trees, 
say, those of 15 years or more, are the only ones noticed with this 
disease." The living portion of the cortex was found to be very 
densely infested with mature females of Heterodera radicicola. It 
seems probable that these nematodes must have passed upward 
through the soft tissue of the cortex from some original infection in 
the root. It is worthy of note that sometimes in herbaceous plants, 
such as tomato, the writer has found nematodes 6 inches or more 
above the level of the ground within the cortical tissue of the stem. 

i Science, n. s., vol. 34, no. 865, July 28, 1911, p. 127. 
217 



BIBLIOGRAPHY. 

Papers seen by the author are indicated by an asterisk (*). 
All not so marked have been accepted on the authority of other 
writers. Only those titles to which reference has been made in the 
text are included in this list. This is not, therefore, a complete 
bibliography of all papers pertaining to tins nematode. 

Abbey, G. Eelworm destruction. Journal of Horticulture, London, ser. 3, vol. 36, 
January 6, 1898, p. 16. 

Eelworm in vine roots. Journal of Horticulture, London, ser. 3, vol. 38, Janu- 
ary 5, 1899, pp. 14-15, figs. 3-4. 

* Atkinson, George F. A preliminary report upon the life history and metamor- 

phoses of a root-gall nematode, Heterodera radicicola (Greeff ! ) Mull., and the injuries 
caused by it upon the roots of various plants. Science Contributions from the 
Agricultural Experiment Station, Alabama Polytechnic Institute, Auburn, Ala., 
vol. 1, no. 1, December, 1889; Bulletin of Agricultural Experiment Station, n. s., 
no. 9, 1889, 54 pp., 6 pis. 

* Diseases of cotton, Bulletin 33, Office of Experiment Stations, U. S. Dept. 

of Agriculture, 1896, pp. 279-316. 

* Bailey, L. H. Some troubles of winter tomatoes. Bulletin 43, Cornell Agricul- 
tural Experiment Station, 1892. 

* Plant -breeding; being six lectures upon the amelioration of domestic plants, 

4th ed., New York, 1906, 483 pp., illustrated. 

Baker, H. Employment for the microscope, London, 1753, chap. 4, p. 250. 

Barber, C. A. A tea-eelworm disease in South India. Department of Land Rec- 
ords and Agriculture, Madras, Agricultural Branch, vol. 2, Bulletin 45, 1901, 
pp. 227-234, 3 pis. 

* Berkeley, M. J. Vibrio forming cysts on the roots of cucumbers. Gardeners' 

Chronicle, London, 1855, p. 220, 2 figs. 

* Bouquet de la Grye. La regeneration des plantations de cafeiers dans les Antilles. 

Bulletin des Seances de la Society Nationale d'Agriculture de France, Paris, vol. 
59, 1899, pp. 683-687. 

* Breda de Haan, J. van. Levensgeschiedenis en bestrijding van het tabaks-aaltje 

(Heterodera radicicola) in Deli. Mededeelingen uit 's Lands Plantentuin, Bata- 
via, 1899, no. 35, pp. 1-69, 3 pis. 

* Wortel-ziekte bij de peper op Java. Verslag omtrent den Staat van 's 

Lands Plantentuin te Buitenzorg over het Jaar 1904, Batavia, 1905, pp. 21-39. 

* Brick, C. Bericht iiber die Tatigkeit der Abteilung fur Pflanzenschutz fur die 
Zeit vom 1 Juli, 1904, bis 30 Juni, 1905. Jahrbuch der Hamburgischen Wissen- 
schaftlichen Anstalten, vol. 22, 1904, p. 299-311. 1905. 

Casali, C. L'Heterodera radicicola Greef nelle radici del nocciuolo. Giornale di 
Viticoltura e di Enologia, vol. 5, 1898, p. 4. 

Chifflot, J. La maladie noire des clematites a grandes fleurs causee par 1' "Hete- 
rodera radicicola Greeff." 1 Semaine Horticole, 1900, pp. 535-537. Bulletin de la 
Society des Sciences Naturelles de Saone-et-Loire, n. s., vol. 6, 1900, pp. 128-134. 

i The name of Greef Is misspelled, as shown In the title of the paper cited. 
217 

76 



BIBLIOGRAPHY. 77 

*Cobb, N. A. Tylenchus and root-gall. The Agricultural Gazette of New South 

Wales, Sydney, 1890, vol. 1, pp. 155-184, figs. 1-8, pi. 4. 
* Root-gall. The Agricultural Gazette of New South Wales, September, 1901, 

vol. 12, no. 9, pp. 1041-1052, figs. 1-8. 
*■ The internal structure of the gall-worm. The Agricultural Gazette of New 



South Wales, Sydney, October, 1902, vol. 13, no. 10, pp. 1031-1033, fig. 1. 
*Cornu, Maxime. Sur une maladie nouvelle qui fait perir les Rubiaeees des serres 
chaudes (Anguillules). Comptes Rendus Hebdomadaires des Seances de l'Academie 
des Sciences, Paris, vol. 88, 1879, pp. 668-670. (1879-1.) 

Etudes surle Phylloxera vastatrix. Memoires Presentes par Divers Savants 
a l'Academie des Sciences de l'lnstitut de France et Imprimes par son Ordre, 
Paris, ser. 2, vol. 26, 1879, pp. 1-357, pis. 1-24. (1879-2.) 

* Cramer, P. J. S. Nematoden in robusta-koffie. Teysmannia, vol. 17, no. 3, 1906, 
pp. 191-192. 

Dalla Torre, K. W. von. Die Zoocecidien und Cecidozoen Tirols und Vorarlbergs. 
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*Darboux, G.,and Houard, C. Catalogue systematique des Zoocecidiesdel'Europe 
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Delacroix, Georges. [Sur quelques maladies vermiculaires des plantes tropicales 
dues a l'Heterodera radicicola Greef.] L'Agriculture Pratique des Pays Chauds, 
vol. 1, 1901-1902, pp. 672-688; vol. 2, 1902-1903, pp. 80-88, figs. 1-2; pp. 135-143. 
Reviewed in Zeitschrift fiir Pflanzenkrankheiten, vol. 14, no. 5, November 1, 
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*Dorsett, P. H. New diseases of the violet. The American Florist, vol. 15, Sep- 
tember 30, 1899, pp. 246-248, figs. 1-5. 

Ducomet, V. Le deperissement des bois de Chene-Liege en Gascogne. Bulletin 
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Dyke, W. Root eelworms in tomatoes and cucumbers. Journal of Horticulture, 
London, ser. 3, vol. 35, December 9, 1897, pp. 547-548. 

* Frank, A. B. [Gallen der Anguillula radicicola Greef an Soja hispida, Medicago 
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Vereins der Provinz Brandenburg, year 23 (1881), Berlin, 1882, pp. 54-55. 

* Ueber das Wurzelalchen und die durch dasselbe verursachten Beschadi- 

gungen der Pflanzen. Landwirthschaftliche Jahrbiicher, vol. 14, 1885, pp. 149-176, 
pi. 3. 

Die Krankheiten der Pflanzen; ein Handbuch fiir Land- und Forstwirte, 



Gartner, Gartenfreunde und Botaniker, 2d ed., vol. 3, Die tierparasitaren Krank- 
heiten der Pflanzen, 1896, chap. 2. 
Galloway, B. T. Club root in roses. American Gardening, vol. 18, February 20, 

1897, p. 127. 
*Gandara, Guillermo. La anguilula del Cafeto. Comisi6n de Parasitologfa Agrf- 

cola, Mexico. Circular 51, 1906, 7 pp., 6 figs. 
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Rio de Janeiro. Archivos do Museu Nacional do Rio de Janeiro, vol. 8, 1892, 

pp. 7-123, pis. 1 to 4, 1 map. 
217 



78 ROOT-KNOT AND ITS CONTROL. 

* Greef, R. [Ueber die frei lebenden Nematoden (Anguillulinen).] Sitzungsbe- 
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* Ueber Nematoden in Wurzelanschwellungen (Gallen) verschiedener 

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landische Cultur, vol. 68, 1890, Erganzungsheft, pp. 49-272. 

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* Enfermedad radicular de la vid causada por la Heterodera radicicola 6 Angui- 

lula radicicola de Greef (Anguilulosis). Boletin del Ministerio de Agricultura, 
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Iggulden, W. Combating eelworms and supporting plants. Journal of Horticulture, 
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* Janse, J. M. De aaltjes-ziekten van eenige cultuurplanten en de middelen ter harer 
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* Jobert, C. Sur une maladie du Cafeier observee au Bresil. Comptes Rendus 
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* Kamerling, Z. Verslag van het Wortelrot-Onderzoek, Soerabaia, 1903, 209 pp., 
19 pis. 

Kieffer, J. J. Synopsis des Zoocecidies d'Europe. Annales de la Societe Ento- 
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* KiiHN, Julius, and Liebscher, G. Bericht fiber Versuche mit rubenmuden 
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* Kuhn, J. Die Ergebnisse der Versuche zur Ermittelung der Ursache der Ruben- 
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* — Die Wirksamkeit der Nematoden-Fangpflanzen nach den Versuchsergebnis- 

sen des Jahres 1881, op. cit., no. 4, 1882, pp. 1-14, 1 fig. 
* — Bericht fiber weitere Versuche mit Nematoden-Fangpflanzen, op. cit., 

vol. 2, no. 6, 1886, pp. 163-175. (1886-1.) 
* Anleitung zur Bekampfung der Riibennematoden, op. cit., vol. 2, no. 6, 

1886, pp. 176-184, pi. 3. (1886-2.) 
217 



BIBLIOGRAPHY. 79 

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Lagerheim, N. G. von. Baltiska zoocecidier. Arkiv for Botanik, Upsala, 1905, 
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* Lavergne, Gaston. L'anguillule du Chili (Anguillula viala?). Revue de Viti- 
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* Licopoli, G. Sopra alcuni tubercoli radicellari continenti Anguillole. Rendiconto 
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Le galle nella flora di alcune Province Napolitane, Naples, 1877, 4 pis. 

* Lotsy, J. P. Eine amerikanische Nematodenkrankheit der Gartennelke. Zeit- 
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* Lounsbury, C. P. Gall-worms in roots of plants. An important potato pest. 
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Magnus, P. Ueber Wurzeln von Passiflora mit kleinen seitlichen Verdickungen, 
verursacht von Heterodera. Sitzungs-Bericht der Gesellschaft Naturforsehender 
Freunde zu Berlin, November, 1888, no. 9, p. 170. 

* Marcinowski, Kati. Parasitisch und semiparasitisch an Pflanzen lebende Nema- 
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May, J. N. Club roots. American Florist, vol. 3, April 15, 1888, p. 396. 

* Eel worms affecting roses. American Florist, vol. 11, January 25, 1896, 

p. 649. 

* Molliard, Marin. Sur quelques caracteres histologiques des cecidies produites 
par l'Heterodera radicicola Greff - 1 Revue Generale de Botanique, vol. 12, 1900, 
pp. 157-165, 1 pi., 1 fig. 

*Mosseri, Victor. La maladie vermiculaire recemment observee en Egypte sur 
les bananiers, betteraves, etc., causee par l'Heterodera radicicola (Greef-Miiller) 
avec une observation sur les Orobanches. Communication faite a l'lnstitut 
Egyptien au Caire, Cairo, 1903, 40 pp., 3 pis., 4 figs. 

* Muller, Carl. Neue Helminthocecidien und deren Erzeuger. Inaugural dis- 
sertation, Berlin, 1883. 

* Mittheilungen iiber die unseren Kulturpflanzen schadlichen, das Gesch- 

lecht Heterodera bildenden Wiirmer. Landwirthschaftliche Jahrbiieher, vol. 13, 
1884, pp. 1-42, pis. 1-4. 

*Munter, Julius. Ueber Gicht oder das sogenannte Gichtig- oder Radigwerden 
(Nielle) des Weizens und anderer Grasfriichte. Bulletin du Congres International 
de Botanique et d'Horticulture, reuni a Amsterdam les 7, 8, 10 et 11 avril 1865, 
Rotterdam, 1866, pp. 420-429. 

* Neal, J. C. The root-knot disease of the peach, orange, and other plants in Florida, 
due to the work of Anguillula. Bulletin 20, Division of Entomology, U. S. Dept. 
of Agriculture, 1889, 31 pp., 21 pis. 

Needham, John Turberville. An account of some new microscopical discoveries, 

London, 1745. 
* [Lettre en reponse au memoire de Roffredi.] Observations sur la Physique, 

sur l'Histoire Naturelle et sur les Arts, par M. l'Abbe Rozier, vol. 5, 1775, 

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* Oliver, George W. New methods of plant breeding. Bulletin 167, Bureau of 

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* The development of farm crops resistant to disease. Yearbook, U. S. Dept. 

of Agriculture, for 1908, pp. 453-464, pis. 39-40. 1909. 

1 The name Greef is misspelled, as shown in the title of the paper cited. 
91294°— Bui. 217—11 6 



80 ROOT-KNOT AND ITS CONTROL. 

* Osterwalder, Adolf. Nematoden als Feinde des Gartenbaues. Gartenflora. 
Zeitschrift fiir Garten- und Blumenkunde, vol. 50, 1901, pp. 337-346, pi. 1488 
lfig. 

Peglion, V. Malattia del Cyclamen cagionata da Heterodera radicicola. L' Italia 
Agricola, Milan, 1902, vol. 39, pp. 444-445, 1 pi. 

Queva, C. Modifications anatomiques provoquees par 1'Heterodera radicicola M till . 
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* Reed, George M. The development of disease-resistant plants. Second Annual 

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*Ritzema Bos, J. L'Anguillule de la tige (Tylenchus devastatrix Kiihn) et lee 
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3, 1892, pp. 161-348, 545-588, pis. 1-10, 3 figs. 

* Les nematodes parasites des plantes cultivees. Sixieme Congres Interna- 
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* Rolfs, P. H. Report of the botanist and entomologist, Florida Agricultural Experi- 
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* Diseases of the tomato. Bulletin 47, Florida Agricultural Experiment Sta- 
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* Selb y, A. D. Investigations of plant diseases in forcing house and garden. Bulletin 
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5 figs. 

* ■ Soil treatment for the forcinghouse. The control of rosette (Rhizoctonia) 

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Bulletin 165, Bureau of Plant Industry, U. S. Dept. of Agriculture, 1909, 74 pp., 

6 figs. 

Stift, A. Bekampfung der Rubennematoden durch Ueberflutung des Feldes. 

Wiener Landwirtschaftliche Zeitung, vol. 53, 1903, pp. 621-622. 
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fiir Bakteriologie, Parasitenkunde und Infektionskrankheiten, pt. 2, vol. 21, 1908, 

no. 4-6, pp. 117-143. 
217 



BIBLIOGRAPHY. 81 

* Stone, G. E. Freezing, steaming and drying soil to destroy eel worms. The 
American Florist, vol. 15, August 12, 1899, pp. 32-33. 

* Stone, G. E., and Smith, R. E. Nematode worms. Bulletin 55, Hatch Experi- 
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* Strubell, Adolf. Unte»uchungen iiber den Bau und die Entwicklung des Riiben- 

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* Tarnani, J. Ueber Vorkommen von Heterodera schachtii Schmidt und H. radici- 
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* Tischler, G. Ueber Heterodera-Gallen an den Wurzeln von Circaea lutetiana L. 
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sammlungs-heft, 1902, pp. 95-107, pi. 25, and 1 text figure. 

* Trelease, William. A nematode disease of the carnation. The American 
Florist, vol. 9, March 1, 1894, pp. 680-681. 

Treub, M. Onderzoekingen over sereh-ziek Suikerriet. Mededeelingen uit 's 

Lands Plantentuin, Batavia, 1885, no. 2, 39 pp. 
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preliminare. Bullettino della Societa Botanica Italiana, 1902, pp. 50-52. 
* Osservazioni e ricerche sulla "malsania" del Nocciuolo in provincia di 

Avellino e sui mezzi atti a combatterla. Redia, vol. 2, 1904, January, 1905, pp. 

37-67. (1905-1.) 
* Nuove osservazioni su Elmintocecidii italiani. Marcellia, vol. 4, 1905, 

pp. 52-54. (1905-2.) 

* Voigt. [No title.] Sitzungsberichte der Niederrheinischen Gesellschaft fur Natur- 
und Heilkunde in Bonn, May 12 and July 7, 1890, pp. 66-74 and 93-98. Verhand- 
lungen des Naturhistorischen Vereines der Preussischen Rheinlande Westfalens 
und des Reg.-Bezirks Osnabriick, vol. 47, 1890. 

Warming, Eug. Knolddannelser paa R0dderne af Elymus arenarius. [In "Smaa 
biologiske og morfologiske Bidrag."] Botanisk Tidsskrift, Copenhagen, 1877-1879, 
ser. 3, vol. 2, pp. 93-96. 

* Webber, H. J., and Orton, W. A. A cowpea resistant to root-knot (Heterodera 
radicicola). Bulletin 17, pt. 2, Bureau of Plant Industry, U. S. Dept. of Agri- 
culture, 1902, pp. 23-38, pis. 5 and 6. 

Wilcox, E. M. Plant breeding to secure resistant forms. Bulletin 123, Office of 
Experiment Stations, U. S. Dept. of Agriculture, 1903, pp. 117-118. 

* Zimmermann, A. Hetvorkomen van Nematoden in dewortels van sirih en thee. 
Teysmannia, vol. 10, 1899, pp. 230-236. 

* De Nematoden des Koffiewortels II. De Ranker (Rostrellaziekte) van 

Coffea arabica. Mededeelingen uit 's Lands Plantentuin, Batavia, no. 37, 1900, 62 
pp., 21 figs. 
217 



DESCRIPTION OF PLATES. 

Plate I. Stages in the development of Helerodera raditicola (Greef) Mull., etc. Figs. 
1 and 2. — Eggs in two different stages of development, X 350. Fig. 3. — Larva 
immediately after escaping from egg, X 105. Fig. 4. — Anterior portion of 
same, X 410. Figs. 5 to 8. — Developmental stages of larvae before sexual differen- 
tiation is apparent, X 105. Fig. 9. — Molt in which sexual differentiation first 
becomes apparent, female nematodes approaching sexual maturity, X 105. 
Fig. 10. — Sexually mature female nematode, a somewhat more advanced stage 
than shown in figure 9, X 105. Fig. 11.- — Posterior portion of sexually mature 
female nematode somewhat compressed, X 220: a, Anal opening; b, alimentary 
canal; c, genital opening; d, vagina; e, e, uteri; /, /, ovaries. Fig. 12. — Egg- 
bearing female nematode, X 47: a, Alimentary canal; b, loop of uterus; c, 
genital opening. Fig. 13. — First visible stage in differentiation of the male 
nematode (compare with fig. 9), X 105: t, t, Testis. Fig. 14. — Mature male still 
within larval skin, X 85. Fig. 15. — Mature male, X 85. Fig. 16. — Anterior 
portion of adult male, showing spear and peculiar structure for guiding its 
movements, X 930. Fig. 17. — Larva entering root of clover, X 100. Fig. 18. — 
Larva of Heterodera schachtii Schmidt just escaped from egg (compare fig. 3), 
X 105. Fig. 19. — Anterior portion of same, X 435. 

Plate II. Fig. 1. — Root-knot on sugar beets grown at the Subtropical Laboratory, 
Miami, Fla. 1907. Photographed by E. A. Bessey. Fig. 2. — Root-knot on 
squash, from Beeville, Tex. 1904. Photographed by W. A. Orton. 

Plate III. Fig. 1. — Root-knot on carrot, from Morrison, 111. 1908. Photographed 
by W. W. Gilbert. Fig. 2. — Root-knot on red clover grown in a pot of sterilized 
soil inoculated with affected roots of Ipomoea syringaefolia, Subtropical Labora- 
tory, Miami, Fla., 1908. Photographed by E. A. Bessey. 
217 
82 



Bui. 217, Bureau of Plant Industry, U. S. Dept. of Agriculture. 



Plate I. 




Stages in the Development of Heterodera Radicicola (Greef) Mull., etc. 



Bui. 217, Bureau of Plant Industry, U. S. Dept. of Agriculture. 



Plate II. 




Fig. 1.— Root-Knot on Sugar Beet. 




Fig. 2.— Root-Knot on Squash. 



Bui. 217, Bureau of Plant Industry, U. S. Dept. of Agriculture. 



Plate III. 




Fig. 2.— Root-Knot on Clover. 



INDEX. 



Page. 

Abbey, G., on control of root-knot 55-56, 76 

Africa, German East, occurrence of root-knot 23 

occurrence of root-knot 23, 25, 38, 42 

South, occurrence of root-knot 23, 38, 42 

Agrostis alba. See Redtop. 

Air, conditions favorable to root-knot 42-44 

See also Moisture, and Temperature. 

Alabama, occurrence of root-knot 23, 64 

Alexandria, Va., investigations of root-knot 47 

Alfalfa, susceptibility to root-knot 17, 24, 43 

Algeria, occurrence of root-knot 23 

Amaranthus spp., susceptibility to root-knot 12, 69 

Ammonium silicofluorid, application for control of root-knot 55-56 

sulphate, application for control of root-knot 54-56, 57, 58 

Andropogon spp., susceptibility to root-knot 12, 21 

Anguillula spp., synonyms of parasite causing root-knot 8, 9, 71 

Animals, agency in spreading root-knot 38, 73 

Aphelenchus sp. , vitality tests 30 

Apple, susceptibility to root-knot 17, 24 

Argentina, occurrence of root-knot 23, 42, 61 

Arizona, occurrence of root-knot 23, 24, 38, 42, 49, 59 

Arkansas, occurrence of root-knot 24 

Asia, occurrence of root-knot 23, 25, 49 

Asparagus, susceptibility to root-knot 12, 38 

Atkinson, G. F., on root-knot 9, 11, 12, 13, 16, 17, 18, 19, 20, 32, 35, 36, 76 

Australia, occurrence of root-knot 23 

Austria, occurrence of root-knot 23 

Bailey, L. H., on methods of control of root-knot 43, 72, 76 

Baker, H., on occurrence of nematodes 30, 76 

Barber, C. A., on occurrence of root-knot 13, 14, 20, 76 

Barley, susceptibility to root-knot 16, 21 

Beaded root-knot. See Root-knot, beaded. 

Bean, experiments for control of root-knot. . . 54, 55, 56, 57, 62, 66, 68 

horse, susceptibility to root-knot 20, 22 

velvet, susceptibility to root-knot 20, 21, 65-67, 70, 74 

Beet, sugar, affected with root-knot, analyses, study 40-41 

nematode. See Heterodera schachtii. 

susceptibility to root-knot 12, 39, 40-41, 52, 57, 61, 82 

tiredness, disease due to Heterodera schachtii 61 

Beggarweed, Florida, resistance to root-knot 17, 65-67, 69, 70, 74 

Berkeley, M. J., on occurrence of root-knot 8, 14, 23, 76 

Bessey, E. A., investigations of root-knot 82 

Bibliography, partial, of root-knot 76-81 

Bidens spp. , resistance to root-knot 21 

Big-root, variant name for root-knot 7 

Bouquet de la Grye, on susceptibility of Coffea spp. to root-knot 14, 71, 76 

Brazil, occurrence of root-knot 9, 23, 49 

Breda de Haan, J. van, on root-knot 11, 12, 13, 14, 16, 17, 18, 19, 54, 76 

Breeding. See Root-knot, breeding resistant strains. 

Brick, C, on occurrence of root-knot 16, 76 

Bromus schraderi, resistance to root-knot 21 

Calcium carbid, use in experiments for control of root-knot 51, 54 

California, occurrence of root-knot 23, 24, 36, 38, 42, 49, 59 

Cane, sugar, susceptibility to root-knot 8, 19 

217 83 



84 ROOT-KNOT AND ITS CONTROL. 

Page. 

Cape Colony, occurrence of root-knot 23 

Carbon bisulphid, use in experiments for control of root-knot. . 47, 49-50, 51-52, 53, 74 
Careless weed. See Amaranthusspp. 

Carrot, susceptibility to root-knot 14, 82 

Casali, C, on occurrence of root-knot 14, 76 

Catalpa, susceptibility to root-knot 13, 22 

Ceylon, occurrence of root-knot 23, 49 

Chambers, W. E., drawings illustrating root-knot nematode 28, 29 

Chemicals, use in experiments for control of root-knot 49-52, 53-56, 74 

Chifflot, J., on occurrence of root-knot 14, 76 

Chile, occurrence of root-knot 9, 23, 42, 61 

China, occurrence of root-knot 23, 25 

Climate, relation to root-knot 24, 42-44, 48, 73 

Clover, Japan, resistance to root-knot 16, 69 

Mexican, employment for reduction of root-knot 69 

species resistant to root-knot 63, 69 

susceptibility to root-knot 16, 17, 20, 22, 43, 69, 82 

Club-root, variant name for root-knot 8 

Cobb, N. A., on root-knot 9, 12, 19, 20, 28, 35, 38-39, 42, 61, 77 

Cobey, W. W., and Shamel, A. D., on strains of tobacco resistant to root-knot . 71, 80 

Coffee, susceptibility to root-knot 9, 14, 49, 50, 60, 71, 75 

Colorado, occurrence of root-knot 24, 40 

Connecticut, occurrence of root-knot 24 

Corn, Indian, resistance to root-knot 21-22 

Cornu, Maxime, on occurrence of root-knot 8, 14, 16, 17, 19, 20, 21, 77 

Cotton, relation to root-knot 15, 66, 67 

Cowpea, relation to root-knot 21, 22, 23, 54-57, 62, 65, 66, 68-69, 70, 71 

Crab-grass, susceptibility to root-knot 21, 65, 69 

Cramer, P. J. S., on occurrence of root-knot 14, 77 

Crops, nonsusceptible, rotations for control of root-knot 65-69, 74 

perennial, root-knot, control in field 48-52, 74 

trap, use in control of root-knot 61-63, 75 

Cucumber, susceptibility to root-knot 14, 22, 59 

Dalla Torre, K. W. von, on occurrence of root-knot 12, 19, 77 

Darboux, G., and Houard, C, on occurrence of root-knot 13, 14, 16, 19, 77 

Davaine, C. J., on occurrence of nematodes 30, 77 

Delacroix, Georges, on occurrence of root-knot 17, 18, 77 

Delaware, occurrence of root-knot '24 

Dorsett, P. H., on occurrence of nematodes 30, 77 

Drying, effect on root-knot, investigations 30, 37-38, 42-44, 45, 48, 60-61, 73, 74, 75 

Ducomet, V., on occurrence of root-knot 19, 77 

Dyke, W. , on control of root-knot 56, 77 

East Indies, occurrence of root-knot 23, 25, 49, 54 

Echinochloa frumentacea. See Millet, Japanese. 

Eel worm, variant name for nematode causing root-knot 7 

Egg of root-knot nematode. See Heterodera radicicola, egg. 

Egypt, occurrence of root-knot 23 

Elm, European, susceptibility to root-knot 20, 39 

England, occurrence of root-knot 23 

Escobar, Romulo, on root-knot infestation of watermelon 40 

Euchlaena luxurians, resistance to root-knot 21 

Europe, occurrence of root-knot 23 

European elm. See Elm, European. 

Eustachys petraea, unaffected by root-knot 21 

Everglades, occurrence of root-knot 42, 59 

Experiments, cross inoculation, for testing adaptation of root-knot nema- 
tode 22-23,82 

See also Root-knot, methods of control. 

Fallow, bare, use in control of root-knot 64, 69, 70, 74 

Fawcett, G. L., on root-knot infestation of the coffee tree 7.5 

Fertilizers, use in control of root-knot in fields 52, 56-58, 70, 74-75 

Fields, root-knot eradication and control 48-71, 74-75 

217 






INDEX. 85 

Page. 

Fig, relation to root-knot 15, 22, 23, 24, 36, 38, 49, 71, 73 

Flooding, method of control of root-knot. 42, 52, 58-60, 70, 74, 75 

Florida beggarweed. See Beggarweed, Florida. 

occurrence of root-knot 9, 

11, 23, 25, 31, 35, 42, 43, 49, 51, 53, 57, 59, 60, 63, 64, 73, 82 

root-knot investigation. See Miami, Fla. 
Formaldehyde, use in experiments for control of root-knot. . . . 46^48, 50-51, 53-54, 74 
Formalin. See Formaldehyde. 
France, experiments for control of phylloxera 54 

occurrence of root-knot 23 

Frank, A. B., on root-knot 8, 12-20, 26, 37, 40, 41, 42, 43, 60, 62, 63, 77 

Freezing. See Temperature. 

Galloway, B. T., on occurrence of root-knot 44, 77 

Galls, root-knot, depth of occurrence in soil 41, 52 

description 7-8, 39^1 

Gammie, G. A., on occurrence of root-knot 13, 16, 17, 20 

Gandara, Guillermo, on occurrence of root-knot IS, 50, 51, 54, 61, 77 

Gardens, in Florida, root-knot investigations 9-10, 31, 43, 51, 53, 55, 82 

Georgia, occurrence of root-knot 23, 59, 64 

German East Africa. See Africa, German East. 

Germany, occurrence of root-knot or other nematodes 8, 23, 26, 52, 57, 69 

Gilbert, W. W., on studies of root-knot 63, 77, 82 

Ginseng, occurrence of root-knot 18, 22, 24, 38, 43, 73 

Gnaphalium purpureum, resistance to root-knot 21 

Goldi, E. A., on root-knot parasite of coffee : . . . 9, 60, 77 

Grains, relation to control of root-knot 21-22, 74 

See also Barley, Corn, Oats, Rye, Wheat, etc. 

Gram, green, susceptibility to root-knot 18, 22 

Grapevine, relation to root-knot 21, 22, 23, 24, 36, 38, 49, 59, 61, 71, 73 

Grasses, relation to root-knot 8, 11, 12, 13, 14, 15, 18, 21, 65, 69 

Greef, R., on occurrence of root-knot 8, 11, 15, 18, 19, 23, 78 

Greenhouses, methods of control of root-knot 9, 24, 44-48, 74 

Gvozdenovie, Franc, on occurrence of root-knot 13, 78 

Halsted, B. D., on occurrence of root-knot 12, 19, 21, 78 

Hawkins, L. N., on occurrence of root-knot 75 

Hays, "W. M., on plant breeding 72, 78 

Helenium tenuifolium, resistance to root-knot 21 

Henning, Ernst, on root-knot 18, 78 

Heterodera javanica, synonym of H. radicicola 8-9 

radicicola, cause of root-knot, life history, effects, etc 25-41, 72, 82 

egg, description 26-27, 73, 82 

larva, description and habits 27-32, 34, 73, 82 

mature forms, description 32-36, 82 

measurements of eggs, parts, etc 26-29, 32-35, 37 

molting 31-32, 34, 32 

original home 25, 72 

overwintering 36, 73 

similarity to H. schachtii 8, 27, 35, 36-37, 40-41 

synonymy 8-9 

See also Root-knot. 

schachtii, cause of disease of the sugar beet 8, 

25, 27, 35-37, 39, 40-41, 52, 57, 58, 61, 82 

Hieronymus, G., on root-knot 15, 78 

Historical notes on study of root-knot 8-10, 72 

Holland, occurrence of root-knot 23 

Hollrung, on the effect of potash on sugar-beet nematodes 57 

Hook, J. M. van, on root-knot 18, 78 

Hordeum vulgare. See Barley. 
Horse bean. See Bean, horse. 
Host plants. See Plants, host. 

Houard, C, and Darboux, G., on occurrence of root-knot 13, 14, 16, 19, 77 

Huergo, J. M., studies on root-knot in Argentina 42, 61, 78 

Hybridization, plant, authorities, note - 72 

217 



86 ROOT-KNOT AND ITS CONTROL. 

Page. 

Iggulden, W., on control of root-knot 56, 78 

Illinois, occurrence of root-knot 82 

Implements, farm, agency in spread of root-knot 38, 73 

I ndia, occurrence of root-knot 23, 25, 49, 54 

Indiana, occurrence of root-knot 24, 35 

Inoculation, cross experiments with root-knot nematodes 22-23 

Introduction to bulletin 7 

Irish potato. See Potato, Irish. 

Italy, occurrence of root-knot 23 

Jackson, A. D., experiments for control of root-knot (J4, (S8-69 

Janse, J. M., on root-knot 12, 17, 78 

Japan, occurrence of root-knot 23, 25 

clover. See Clover, Japan. 

Java, occurrence of root-knot 8, 23 

Jobert, C, on occurrence of root-knot 14, 78 

Johnson, J. M., assistance in root-knot investigations 10 

grass. See Andropogon. 

Kafir, corn, resistance to root-knot 21 

Kainit, application for control of root-knot 56, 57, 58, 71 

Kamerling, Z., on occurrence of root-knot 13, 78 

Kentucky, probable presence of root-knot 24 

Kieffer, J. J., on root-knot 20,78 

Kuhn, Julius, and Liebscher, G., on occurrence of sugar-beet nematodes 61, 78 

on control of sugar-beet nematodes 61, 78, 79 

Laboratory, Subtropical. See Miami, Fla. 

Lagerheim, N. G. von, on occurrence of root-knot 15, 16, 79 

Larva of root-knot nematode. See Heterodera radicicola, larva. 

Lavergne, Gaston, on root-knot 9, 11, 18, 42, 61, 71, 79 

Lemon, susceptibility to root-knot 11, 14 

Lespedeza spp. (bush and Japan clovers), resistance to root-knot 16, 69 

Lettuce, susceptibility to root-knot 16, 22 

Licopoli, G., on occurrence of root-knot 12, 13, 14, 15, 18, 19, 20, 21, 79 

Liebscher, G., and Kuhn, Julius, on occurrence of sugar-beet nematodes 61, 78 

Lime, use in control of root-knot 54, 55 

Little's soluble phenyl. See Phenyl, Little's soluble. 

Lolium perenne, resistance to root-knot 21 

Loose, J. L., on treatment of roses for root-knot 47-48 

Lotsy, J. P., on occurrence of root-knot 14, 79 

Louisiana, occurrence of root-knot 23, 64 

Lounsbury, C. P., on root-knot 11, 18, 38, 42, 61, 79 

Madagascar, occurrence of root-knot 23 

Magnus, P., on root-knot 18, 79 

Manure, infested, relation to spread of root-knot 39, 73-74 

Marcinowski, Kati, list of plants susceptible to root- knot 10, 11, 79 

Maryland, occurrence of root-knot 24 

May, J. N., on control of root-knot on greenhouse plants 8, 44, 79 

Meloidogyne exigua, synonym of Heterodera radicicola 9 

Mexico, occurrence of root-knot 23, 40, 49, 61 

Miami, Fla., root-knot investigations 9-10, 31, 43, 51, 53, 55, 82 

Michigan, occurrence of root-knot 24, 43 

Millet, Japanese barnyard, resistance to root-knot 21 

Millets, susceptibility to root-knots 13, 15, 21 

Milo, resistance to root-knot 21 

Mississippi, occurrence of root-knot 23, 64 

Moisture, effect on root-knot 42, 73 

See also Drying and Flooding. 

Molliard, Marin, on occurrence of root-knot 12, 79 

Molting. See Heterodera radicicola, molting. 

Monetta, S. C, root-knot investigations 9-10, 43, 53, 54, 55, 56, 62, 65-68 

Morning-glory, tree, susceptibility to root-knot 16, 22, 82 

Mi isseri, Victor, on occurrence of root-knot 13, 15, 19, 79 

Mulberry, susceptibility to root-knot 17, 24, 38, 49, 73 

Midler, C, on root-knot 8, 14, 17, 26, 79 

217 



INDEX. 87 

Page. 

Miinter, Julius, on occurrence of nematodes 30, 79 

Muskmelon, susceptibility to root-knot 14, 22, 59 

Neal, J. C, on occurrence of root-knot 9-21, 25, 69, 79 

Nebraska, occurrence of root-knot 24, 43 

Needham, J. T., on occurrence of nematodes 30, 79 

Nematode parasite. See Aphelenchus, Heterodera, Tylenchus, etc. 

Neocosmospora vasinfecta, wilt fungus, analogy to root-knot 40, 71 

New England, occurrence of root-knot 24 

New Mexico, occurrence of root-knot 23, 42 

New South Wales, occurrence of root-knot 9, 39 

New York, occurrence of root-knot 24, 43 

New Zealand, occurrence of root-knot 23 

North Carolina, occurrence of root-knot 23, 64 

Nursery, relation of stock to root-knot introduction 24, 38, 73 

Oats, resistance to root-knot 12, 21, 65-67, 74 

Ohio Agricultural Experiment Station, investigations of root-knot 46-47 

Oklahoma, probable presence of root-knot 24 

Okra, susceptibility to root-knot 11, 54, 55, 56, 62, 66, 68 

Oliver, G. W., on plant breeding 72, 79 

Orange, susceptibility to root-knot 11, 14 

Orchards, treatment with carbon bisulphid for root-knot 49-50, 74 

Orton, W. A., and Webber, H. J., on resistance of cowpeas to root-knot. ... 65, 71, 81 

on studies relating to root-knot 40, 72, 79, 82 

Osterwalder, Adolf, on occurrence of root-knot 14, 80 

Panicum miliaceum. See Proso. 

Papaya, susceptibility to root-knot 13, 22, 49, 50, 51 

Parasites, nematode. See Aphelenchus, Heterodera, and Tylenchus. 

Pea, susceptibility to root-knot ." 18, 33 

Peach, susceptibility to root-knot 12, 23, 24, 38, 49, 59, 73 

Peanut, susceptibility to root-knot 12, 65, 74 

Peglion, V., on occurrence of root-knot 14, 80 

Pennisetum sp., resistance to root-knot 21 

Pennsylvania, occurrence of root-knot 24 

Peony, susceptibility to root-knot 18, 43 

Phenyl, Little's soluble, use in experiments for control of root-knot 56 

Philippines, probable presence of root-knot 23 

Phleum pra tense. See Timothy. 

Phosphate, acid, use for control of root-knot 56 

Phylloxera, measures for control as related to root-knot 49, 50, 51, 54, 71 

Piper, C. V., on susceptibility of Stizolobium pruriens to root-knot 20, 21 

Plants, crop, resistant to root-knot 21-22, 65-69 

greenhouse, treatment for root-knot 47^8, 74 

host, effects of attack of the root-knot parasite 7-8, 39-41, 71 

parts attacked by the root-knot parasite 7-8, 39^0, 75 

susceptibility to root-knot 10-21, 72 

Plates, description 82 

Potash in fertilizers, effect on root-knot in fields 52, 56-58, 70-71, 74-75 

Potassium magnesium carbonate, effect on root-knot 56, 57, 58, 71 

sulphate, effect on root-knot 56, 57, 58, 71 

sulphocarbonate, experiments for control of root-knot 50, 54 

Potato, Irish, root-knot infestation and spread 19, 38-39, 40, 69, 70, 73 

sweet, susceptibility to root-knot 16, 31 

Proso, resistance to root-knot 21 

Purslane, susceptibility to root-knot 19, 22 

Queva, C, on occurrence of root-knot 14, 80 

Quicklime. See Lime. 

Radish, susceptibility to root-knot 19, 40 

Rape, summer, use as trap crop for control of sugar-beet nematodes 61-62 

susceptibility to root-knot 13 

Redtop, resistance to root-knot 21 

Reed, G. M., on plant breeding 72, 80 

Resistant strains. See Root-knot, breeding. 

217 



88 ROOT-KNOT AND ITS CONTROL. 

Page. 

Rhizoctonia, presence in plants treated for root-knot 54 

Rhode Island, occurrence of root-knot 24 

Ritzema Bos, J., on root-knot 15, 20, 22, 30, 80 

Rolfs, P. H., on root-knot 11, 17, 20, 21, 42, 60, 61, 65, 69, 80 

Root-gall, variant name for root-knot 7 

Root-knot, beaded, variant name for root-knot 7 

bibliography 8, 76-81 

breeding resistant strains of plants 71-72, 75 

causal parasite 25-41, 72, 82 

cross-inoculation experiments 22-23, 82 

depth of galls below surface of soil 41, 52 

favoring conditions of soil, moisture, etc 41-44, 73 

geographic distribution 7, 8-9, 23-25, 72 

historical notes 8-10, 72 

manner of introduction 23, 24-25, 37-39, 73-74 

methods of control 44-72, 74-75 

plants affected 10-21, 72 

symptoms, description .' 7-8 

variant names 7, 8-9 

vitality 22-23, 30, 42, 43-44 

Rootlets, formation above root-knot galls 39-40 

Root-rot, tobacco, control by steam sterilization 63-64 

Roots, swellings. See Galls. 

Rose, susceptibility to root-knot 8, 19 

treatment for root-knot 47-48 

Ross, Hermann, on occurrence of root-knot 12, 17, 20, 80 

Rotations, crop, for root-knot control, experiments 65-69, 74 

Rubenmiidigkeit (beet tiredness), due to a nematode 61 

Rudd, W. N., on occurrence of root-knot in greenhouses 44, 80 

Russia, occurrence of root-knot 23 

Rye, relation to control of root-knot 21, 65-69, 74 

Sahara (oases), occurrence of root-knot 23 

Sainfoin, susceptibility to root-knot 8, 17 

Salmon, E. S., on plant-breeding as related to plant disease 72, 80 

Schlechtendal, D. H. R. von, on occurrence of root-knot 14, 80 

Schroeder, C, on control of Tylenchus dipsaci 69, 80 

Secale cereale. See Rye. 

Seed beds, methods for control of root-knot 44-48, 74 

selection. See Selection. 

Selby, A. D., on occurrence of root-knot 12, 17,19,44,46-47,80 

Selection, method for production of resistant plants 72, 75 

Shamel, A. D., and Cobey, W. W., on strains of tobacco resistant to root-knot. . 71, 80 

method of sterilizing soil 63 

Sheldon, J. L., on occurrence of root-knot 20, 80 

Skeels, H. C, revision of names in list of plants susceptible to root-knot 10 

Smith, R. E., and Stone, G. E., on root-knot 9, 15, 16, 22, 26, 27, 31, 36, 44. 45, 81 

Soil, character, effect upon root-knot 23, 41, 48, 73 

fresh, use for control of root-knot nematodes 45-46, 74 

infested, agency in spreading root-knot 37-39, 73-74 

treatment for eradication of root- knot 22, 44—46, 48, 63-64, 74 

Solidago spp., resistance to root-knot 21 

Sorauer, P., on root-knot 17, 19, 20, 80 

Sorghum, resistance to root-knot 21 

South Africa. See Africa, South. 

South America, occurrence of root-knot 9, 23, 42, 49, 61 

South Carolina, occurrence of root-knot. . 9-10, 23, 35, 43, 53-56, 57, 58, 62, 64, 65-68, 73 
root-knot investigations. See Monetta, S. C. 

Spillman, W. J., on plant breeding 72, 80 

Squash, susceptibility to root-knot 14, 22, 55, 56-57, 82 

Steam, live, use for control of root-knot 44-45, 46, 63-64, 74 

Sterilization, soil, for control of root-knot 22, 44-45, 63-64, 74 

Stift, A., on control of sugar-beet nematode 57, 59, 80 

Stone, G. E., and Smith, R. E., on root-knot 9,15,16,22,26,27,31,36,44,45,81 

on methods for control of root-knot 60, 81 

Strawberry, susceptibility to root-knot 15, 22, 38 

217 



INDEX. 89 



Strubell, Adolf, study of Heterodera schachtii 27, 35, 81 

Sturgis, W. C, on occurrence of root-knot 12, 81 

Subtropical laboratory. See Miami, Fla. 
Sugar cane. See Cane, sugar. 

Sumatra, occurrence of root-knot 23 

Summary of bulletin 72-75 

Sunflower, susceptibility to root-knot 15, 22 

Susceptibility to root-knot, list of plants subject to attack 10-21, 72 

Sweden, occurrence of root-knot 23 

Sweet potato. See Potato, sweet. 

Swellings, root-knot. See Galls. 

Symptoms of root-knot. See Root-knot, symptoms. 

Syntherisma sanguinalis. See Crab-grass. 

Tarnani, J., on occurrence of root-knot 15, 18, 20, 81 

Tea, susceptibility to root-knot 20, 49 

Temperature, conditions favorable to development of root-knot 24, 42-44, 73, 74 

Tennessee, probable presence of root-knot 24 

Texas, occurrence of root-knot 23, 24, 38, 64, 82 

Thielavia, root-rot of tobacco, control by sterilization 63-64 

Thornber, J. J., on occurrence of root-knot 16 

Timothy, resistance to root-knot 21 

Tischler, G., on root-knot 14, 39, 81 

Tobacco, susceptibility to root-knot 17, 22, 71 

Tomato, susceptibility to root-knot 17, 22, 40, 54, 55, 56, 62, 66, 68, 69 

Transvaal, occurrence of root-knot 23 

Trap crops. See Crops. 

Trelease, William, on occurrence of root-knot 14, 81 

Treub, M., on root-knot of sugar cane 8, 81 

Trotter, Alessandro, on root-knot 12, 13,14, 15,16,17,19,81 

Tylenchus hordei, cause of root-gall of Elymus arenarius 15 

spp., comparison with Heterodera radiciola 22, 29, 30, 69 

synonyms for Heterodera radicicola 9 

Typha latifolia, susceptibility to root-knot 75 

Utah, occurrence of root-knot 24, 36 

Vehicles, wheels, agency in spread of root-knot 38, 73 

Velvet bean. See Bean, velvet. 

Violet, susceptibility to root-knot 8, 21, 30 

Virginia, occurrence of root-knot 24, 4i 

Voigt, description of egg sack of sugar-beet nematode 16, 20, 27, 37, 87 

Walnut, susceptibility to root-knot 16, 49 

Warming, Eug., on occurrence of root-knot 15, 81 

Washington, D. C, investigations of root-knot 9, 21, 38 

Water, running, agency in spread of root-knot 37 

Watermelon, susceptibility to root-knot 14, 40, 59, 71 

Webber, H. J., and Orton, W. A., on resistance of cowpeas to root-knot 65, 71, 81 

on occurrence of root-knot in Florida 11 

Weeds, danger of harboring root-knot 68-69, 70 

Wester, P. J., assistance in root-knot investigations 10 

West Indies, occurrence of root-knot 25, 23 

West Virginia, presence of root-knot 24, 43 

Wheat, susceptibility to root-knot 20, 21, 74 

Wilcox, E. M., on plant breeding 72, 81 

Wimmer, on the effect of nematodes on the sugar beet 57-58 

Wind, agency in spread of root-knot 37-38 

Winterhalter, W. K., analyses of sugar beets affected with root-knot 40-41 

Wintering of root-knot. See Heterodera radicicola, overwintering. 

Woods, A. F., investigations of root-knot 47 

Yuma, Ariz., investigations of root-knot 59 

Zimmermann, A., on occurrence of root-knot 11, 18, 81 

Zinnia spp., resistance to root-knot 21 

217 

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LB '12 






& 




